Piezoelectric/electrostrictive device having mutually opposing thin plate portions

ABSTRACT

A piezoelectric/electrostrictive device including a driving portion, a movable portion, a fixing portion for holding the driving portion and the movable portion, the movable portion being coupled with the fixing portion via the driving portion, and a hole formed by inner walls of the driving portion, movable portion, and fixing portion. The driving portion includes a pair of mutually opposing thin plate portions and a piezoelectric/electrostrictive (P/E) element. A P/E operating portion of the P/E element is arranged on at least a part of an outer surface of at least one of the thin plate portions, such that one end thereof exists on the fixing portion or the movable portion and the other end thereof is arranged on the thin plate portion. At least one end of a P/E layer of the P/E element exists on the fixing portion or the movable portion, and the other end is arranged on the thin plate portion. The Young&#39;s modulus Y 1  of a material composing the thin plate portions and the Young&#39;s modulus Y 2  of a material composing the P/E layer have a relationship satisfying 1&lt;Y 1 /Y 2 ≦20.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a piezoelectric/electrostrictive devicecomprising a movable portion being operated based on a displacement of apiezoelectric/electrostrictive element, or to apiezoelectric/electrostrictive device capable of detecting adisplacement of a movable portion by a piezoelectric/electrostrictiveelement, and more particularly relates to apiezoelectric/electrostrictive device which is superior in mechanicalstrength, impact resistance, and humidity resistance, and capable ofhaving the movable portion efficiently operated with large magnitudesubstantially in parallel toward the direction of a specific axis.

In recent years, in the fields of optics, magnetic recording, precisionmachining, and the like, a displacement element capable of adjusting anoptical path length or a position in sub-micron order has been required,and development has been progressed of a displacement element utilizinga displacement due to the inverse piezoelectric effect or theelectrostrictive effect caused when a voltage is applied to apiezoelectric/electrostrictive material (for example, a ferroelectricsubstance or the like). For example, as shown in FIG. 27, apiezoelectric actuator 21 is disclosed, in which, by providing a hole 28on a board-like shaped body composed of a piezoelectric/electrostrictivematerial, a fixing portion 25, movable portion 24, and a beam 26connecting therewith are integrally formed, and the beam 26 is furtherprovided with an electrode layer 22 (See JP-A-10-136665).

In the actuator 21, when a voltage is applied across the electrode layer22, the beam 26 expands or contracts, in a direction in which the fixingplate 25 is connected with the movable portion 24, by the inversepiezoelectric effect or the electrostrictive effect, thus enabling themovable portion 24 to have an arc-shaped displacement or a rotationaldisplacement in-plane of the board-like shaped body. On the other hand,JP-A-63-64640 discloses a technique with regard to an actuator utilizinga bimorph, wherein an electrode of the bimorph is split, and by drivingthe actuator by selecting the split electrodes, precise positioning canbe performed at a high speed, and, for example, a structure for usingtwo bimorphs opposed to each other is shown in the specificationthereof.

However, in the above-described actuator 21, as the displacement in anexpanding or contracting direction (namely, in-plane direction of theboard-like shaped body) of a piezoelectric/electrostrictive material istransmitted per se to the movable portion, there is a problem that anoperational quantity of the movable portion 24 is small. Moreover, theactuator 21, having all the members thereof being composed of apiezoelectric/electrostrictive material which is fragile andcomparatively heavy, has another problem that the actuator 21 per se isheavy and operationally likely to be influenced by harmful vibrations(for example, residual vibrations or noise vibrations when operated at ahigh speed), in addition to being low in mechanical strength, andinferior in handling, impact resistance, and humidity resistance.

In order to solve the above-described problems in the actuator 21, aproposition has been made that a filler having plasticity is filled inthe hole 28. However, when the filler is used, it is apparent that theefficiency of the displacement due to the inverse piezoelectric effector the electrostrictive effect is reduced.

On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is that, inbonding a relaying member 3 with a bimorph, a portion without a splitelectrode is joined with the relaying member, and at the joined portion,the effect of the split electrode is unable to be utilized, in otherwords, merely a bimorph portion which is not a displacement generatingportion is joined. Further, a portion where a head is joined with abimorph is joined in a similar bonding mode. As the result, a bendingdisplacement of the bimorph is developed toward the inner space betweenthe relaying member and the head, and the structure is that an actionfor effectively displacing the head per se toward the outer space isunable to be obtained. In addition, the actuator disclosed inJP-A-63-64640 is so structured that a displacement generating member anda so-called frame member (relaying member, or the like) are separatelyprepared, and then adhered to be incorporated, and consequently thestructure is that the joined state of the frame with the bimorph islikely to vary with time in accordance with operation of the bimorph,and that drifting of the displacement, exfoliation, or the like is alsolikely to be caused. Furthermore, a structure having an adhesive agentat a joined portion of the bimorph with the relaying member and at ajoined portion of the head with the bimorph, namely at a holding portionof a displacement member, is low in stiffness compared to the holdingportion per se, and thus an increase in the resonant frequency which isrequired in high speed operation is difficult to be obtained.

Of course, the applicant of the present invention and the others havemade a proposition of a piezoelectric/electrostrictive device capable ofsolving such problems in the specification of Japanese PatentApplication No. 11-375581, or the like. However, apiezoelectric/electrostrictive device which is capable of furtherincreasing the displacement quantity of a movable portion, and makingthe displacement path of the movable portion substantially parallelrelative to the fixing portion, is sought after specifically as aprecise positioning device in the fields of magnetic recording andoptics.

The present invention is made in view of the above-described currentsituation, and an object thereof is to provide a displacement elementwhich is capable of further increasing displacement quantity of themovable portion and making a displacement path of the movable portionsubstantially in parallel relative to the fixing portion withoutreducing resonance frequency, and a sensor element capable of detectingvibrations of the movable portion in high precision.

SUMMARY OF THE INVENTION

According to the present invention, firstly provided is apiezoelectric/electrostrictive device comprising a driving portion to bedriven by a displacement of a piezoelectric/electrostrictive element, amovable portion to be operated based on displacement of the drivingportion, and a fixing portion for holding the driving portion and themovable portion, the movable portion being coupled with the fixingportion via the driving portion, and a hole being formed by inner wallsof the driving portion, an inner wall of the movable portion, and aninner wall of the fixing portion, and the piezoelectric/electrostrictivedevice is characterized in that the driving portion comprises a pair ofmutually opposing thin plate portions, and apiezoelectric/electrostrictive element including apiezoelectric/electrostrictive operating portion comprising a pair ormore of electrodes and a piezoelectric/electrostrictive layer arrangedon at least a part of the outer surface of at least one thin plateportion out of the thin plate portions, one end of thepiezoelectric/electrostrictive operating portion in a direction in whichthe fixing portion is connected with the movable portion exists on thefixing portion or the movable portion, and the other end of thepiezoelectric/electrostrictive operating portion is arranged on the thinplate portion, and at least one end of thepiezoelectric/electrostrictive layer of thepiezoelectric/electrostrictive element exists on the fixing portion orthe movable portion, and the other end thereof is arranged on the thinplate portion, and the Young's modulus Y1 of a material composing thethin plate portions and the Young's modulus Y2 of a material composing amaterial of the piezoelectric/electrostrictive layer have a relationshipthat satisfies the following expression, namely;

1<Y1/Y2≦20.

Here, so long as being within a range satisfying the relationship of theYoung's moduli described above, the movable portion, the thin plateportions, and the fixing portion may be composed of a ceramic or ametal, or respective members may be mutually composed of ceramicmaterials, or metallic materials, or may be composed as a hybrid bycombining the members fabricated with ceramic materials and the membersfabricated with metallic materials.

Further provided are a piezoelectric/electrostrictive devicecharacterized in that a movable portion, thin plate portions, and afixing portion are integrally formed by a ceramic green sheet laminatedbody being simultaneously sintered, a piezoelectric/electrostrictivedevice characterized in that a piezoelectric/electrostrictive elementhas a film-like piezoelectric/electrostrictive element directly formedon the thin plate portion and the movable portion or the fixing portion,and integrally formed by having them sintered, and apiezoelectric/electrostrictive device characterized in that thepiezoelectric/electrostrictive layer of the film-likepiezoelectric/electrostrictive element does not contain any glass frit.

Further provided are a piezoelectric/electrostrictive device wherein amovable portion displaces so as to satisfy an expression of;

0°≦θ≦0.1°

relative to an angle θ formed by a side of the movable portion, opposingto the fixing portion, in a displaced state and the same side of themovable portion prior to the displacement, apiezoelectric/electrostrictive device characterized in that the length Lof a portion arranged on the thin plate portion out of thepiezoelectric/electrostrictive operating portion satisfies the followingexpression, relative to the length e of the thin plate portion and thethickness d of the thin plate portion, namely;

30≦(L/e)×100≦100≦d/2.5,

and a piezoelectric/electrostrictive device characterized in that, in avirtual circle having the center thereof on a perpendicular dropped fromthe middle point of a side, opposing to the fixing portion, of themovable portion, in a non-displacement state, to the fixing portion,passing through the middle point of the movable portion in thenon-displacement state and the middle point of the movable portiondisplaced by operation of the driving portion, the movable portiondisplaces so as to satisfy the following expression of a relationshipbetween the radius r of the virtual circle and the length e of the thinplate portion, the expression being;

0≦e/r≦100,

and when driven by a displacement of the piezoelectric/electrostrictiveelement, an inflection point of the displacement exists on the thinplate portion.

Further provided in the present invention are apiezoelectric/electrostrictive device characterized in that the length Lof the piezoelectric/electrostrictive operating portion arranged on thethin plate portion satisfies the following expression, in relationshipwith the length e of the thin plate portion and the thickness d of thethin plate portion, the expression being;

40≦(L/e)×100=100−d/1.5,

a piezoelectric/electrostrictive device characterized in that, in avirtual circle having the center thereof on a perpendicular dropped fromthe middle point of a side, opposing to the fixing portion, of themovable portion in a non-displacement state, to the fixing portion, andpassing through the middle point of the movable portion in thenon-displacement state and the middle point of the movable portiondisplaced by operation of the driving portion, the movable portiondisplaces such that a relationship between the radius r of the virtualcircle and the length e of the thin plate portion satisfies thefollowing expression, the expression being;

0≦e/r≦20,

and an inflection point of the displacement of the thin plate portionsexists at a position parted more than one half of the length of the thinplate portion from a joined portion of the fixing portion, or themovable portion with the thin plate portion; thepiezoelectric/electrostrictive operating portion existing on eitherportion of the fixing portion, or the movable portion, and apiezoelectric/electrostrictive device characterized in that, relative tothe thickness a of the hole and the length e of the thin plate portion,the ratio e/a is 0.1 to 2, and relative to the thickness a of the holeand width b of the thin plate portion, the ratio a/b is 0.05 to 2.

Further, a piezoelectric/electrostrictive device of the presentinvention preferably has a movable portion, thin plate portions, and afixing portion, composed of ceramics integrally formed, more preferablyhave the movable portion, the thin plate portions, and the fixingportion, composed of a material containing fully-stabilized zirconia asthe major component, or a material containing partially-stabilizedzirconia as the major component, and most preferably have at least themovable portion, the thin plate portions, and the fixing portion,composed by a sintered ceramic green laminated body. The reason is thatjoined portions with the movable portion, the thin plate portions, andthe fixing portion can be structured to be without boundary by beingintegrated by sintering, thus long term reliability with time of suchportions can be raised, a phenomenon such as drifting or the like asvariation with time of the device by the displacement can be suppressedto be minimum, and a large displacement can be developed with higherreproducibility. On the other hand, when at least the thin plateportions are composed of a metallic material as described previously, adevice superior in the handling property and impact resistance can beprovided.

It should be noted that, when fabricating a device of a structureaccording to the present invention, in addition to the method where allmembers thereof are integrated by sintering, there is a method in that alaminated body split in a mutually opposing direction of the thin plateportions, namely a ceramic laminated body comprising a thin plate and amember having a rectangular fixing portion and movable portion isprepared, a piezoelectric/electrostrictive element is formed by thescreen printing at predetermined positions of the thin plate portion andthe fixing portion or the movable portion, and integrally sintered withthe ceramic laminated body to prepare at least two of the sinteredstructures, and the sintered structures are joined together so as tohave thin plate portions to be parted from each other, namely to havethe above-mentioned members respectively to be a fixing portion and amovable portion mutually matched by use of an adhesive or the like suchas glass or an organic resin. However, a device fabricated first byintegrating the movable portion, the thin plate portions, and the fixingportion by simultaneous sintering, and then apiezoelectric/electrostrictive element film being formed on the sinteredbody, and finally by integrally sintering the body thus formed, ispreferable as the device has no discontinuous portion as a structuresuch as a joined portion where the third party intervenes, thus thedevice thus fabricated is superior in stability and reliability even ifa stress is applied thereon by operation of the driving portion, whichis preferable.

Moreover, in a piezoelectric/electrostrictive device of the presentinvention, it is preferable that a piezoelectric/electrostrictive layerconstituting a piezoelectric/electrostrictive element is composed of amaterial containing lead zirconate, lead titanate, and lead magnesiumniobate as the major component, and a material containing sodium bismuthtitanate as the major component is also preferable. Details of materialsto be used are to be described later.

It should be noted that, in the present specification, a terminology“operate in substantially parallel” means, with reference to FIG. 26,when both ends of the right-hand side and the left-hand side of the holeat the joined portion of the movable portion with both thin plateportions in a state when the device is not driven are respectively setas the point A and the point B, while positions of the both ends in astate when the device is driven at a predetermined voltage are made asthe point C and the point D, a displacement is performed within a rangewhere an angle q to be formed by a segment passing through the point Dand parallel to a segment AB and a segment CD satisfies the followingexpression, namely;

0°≦θ≦0.1°.

For this value, displacement quantities at above-described respectivepoints are measured by the laser Doppler vibrometer (made by GraphtecCorp), and the value is derived by calculating the measured displacementquantities.

In the present invention, “film-like” means what is formed by the thickfilm or thin film forming method, as to be described hereinafter, andordinarily, it is distinguished from the one formed by adheringplate-shaped piezoelectric/electrostrictive elements composed ofpiezoelectric plates by use of an adhesive. Further,“piezoelectric/electrostrictive device (hereinafter simply referred toas “device”) according to the present specification is a notion implyingan element for altematingly converting an electrical energy into amechanical energy by way of a piezoelectric/electrostrictive material.Accordingly, the device can be preferably used as an active element fora variety of actuators, oscillators, and the like, particularly as adisplacement element utilizing a displacement of the inversepiezoelectric effect or the electrostrictive effect, however, it canalso be used as a passive element for an acceleration sensor element, animpact sensor element, or the like.

A piezoelectric/electrostrictive element is an element comprising a pairor more of electrodes and a piezoelectric/electrostrictiveelectrostrictive layer, for being driven based on a signal to betransmitted, and for performing a function of transmitting the movementthereof to the thin plate portions. In the element, apiezoelectric/electrostrictive operating portion is a portion tosubstantially move the piezoelectric/electrostrictive element so as tomove the movable portion in a predetermined operation in accordance witha signal given to said piezoelectric/electrostrictive element, andcomposed of a portion where a pair or more of electrodes and apiezoelectric/electrostrictive layer are mutually overlapped. It shouldbe noted that “having multiple layers of piezoelectric/electrostrictiveoperating portions” means that a plurality ofpiezoelectric/electrostrictive operating portions are arranged in layersin a direction perpendicular to the main surface of the thin plateportions, namely in the thickness direction of the thin plate portions.Respective electrodes which constitute respectivepiezoelectric/electrostrictive operating portions may have a structurebeing shared between operating portions, or a structure made to be incommon use, or a structure to be mutually independent. A predeterminedsignal is transmitted to respective electrodes constituting respectiveoperating portions, and an electric field is applied to apiezoelectric/electrostrictive layer constituting respective operatingportions.

Moreover, “piezoelectric” means “piezoelectric and/or electrostrictive”.“Length” means a distance in a direction in which a movable portion isconnected with a fixing portion, namely in the Z-axis direction indrawings, “width” means a distance in a direction penetrating through ahole, namely in the Y-axis direction in drawings, and “thickness” meansa distance in a direction in which a piezoelectric/electrostrictivedevice is laminated with a thin plate portion, namely in the X-axisdirection in drawings. It should be noted that in drawings those havingthe same or similar function is in principle indicated by the samesymbol.

Inflection point means a point where the bending direction is changed ina bend of the thin plate portion caused by operation of apiezoelectric/electrostrictive element, and this may be described by useof a piezoelectric/electrostrictive element in the left-hand side inFIG. 2(b) that, in the portion lower than the point indicated as theinflection point, the vertex of the bend is oriented toward a hole, andin the portion upper than the point indicated as the inflection point,the vertex of the bend is oriented toward outside, thus forming a bend,and the boundary is the inflection point. Ordinarily, the inflectionpoint exists in the vicinity of the tip of a piezoelectric operatingportion comprising a portion where a pair or more of electrodes and apiezoelectric/electrostrictive layer formed on thin plate portion aremutually overlapped.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic explanatory view describing an operationalstate of a piezoelectric/electrostrictive device of the presentinvention.

FIGS. 2(a) and (b) show schematic explanatory views describing aninflection point in an operational state of apiezoelectric/electrostrictive device of the present invention, and FIG.2(a) shows a state prior to a displacement, with a symbol “e” showing alength of thin plate portions, and FIG. 2(b) shows a state whendisplaced, with a symbol “Li” showing the position of the inflectionpoint.

FIG. 3 shows a schematic explanatory view describing a relationshipbetween a length “L” of the portion of a piezoelectric/electrostrictiveelement arranged on a trim plate portion, a length get of thin plateportion, and a thickness “d” of a thin plate portion, in a structure ofa piezoelectric/electrostrictive device of the present invention.

FIG. 4 shows a schematic perspective view of an embodiment of apiezoelectric/electrostrictive device of the present invention.

FIG. 5 shows a schematic perspective view of another embodiment of apiezoelectric/electrostrictive device of the present invention.

FIG. 6 shows a schematic perspective view of still another embodiment ofa piezoelectric/electrostrictive device of the present invention.

FIGS. 7(a), (b), and (c) show schematic explanatory views describing anarrangement of piezoelectric/electrostrictive elements used in apiezoelectric/electrostrictive device of the present invention.

FIG. 8 shows a schematic perspective view describing a mutualrelationship between respective members of apiezoelectric/electrostrictive device of the present invention.

FIG. 9 shows a schematic perspective view of still another embodiment ofa piezoelectric/electrostrictive device of the present invention.

FIG. 10 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 11 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 12 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 13 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 14 shows a schematic perspective view of an embodiment of apiezoelectric/electrostrictive element constituting apiezoelectric/electrostrictive device of the present invention.

FIG. 15 shows a schematic perspective view of an embodiment of apiezoelectric/electrostrictive element constituting apiezoelectric/electrostrictive device of the present invention.

FIG. 16 shows a schematic perspective view of another embodiment of apiezoelectric/electrostrictive element constituting apiezoelectric/electrostrictive device of the present invention.

FIGS. 17(a) and (b) show schematic explanatory views of an embodiment ofan arrangement method of electrode leads of apiezoelectric/electrostrictive device of the present invention.

FIG. 18(a) and (b) show schematic explanatory views of examples ofceramic green sheets used in fabricating apiezoelectric/electrostrictive device of the present invention.

FIG. 19 shows perspective views exemplarily showing examples ofrespective ceramic green sheets to be used in a ceramic green sheetlaminated body when fabricating a piezoelectric/electrostrictive deviceof the present invention.

FIGS. 20(a), (b), (c), and (d) show process views of an embodiment of amethod of fabricating a piezoelectric/electrostrictive device of thepresent invention.

FIG. 21 shows side views of another embodiment of a method offabricating a piezoelectric/electrostrictive device of the presentinvention.

FIGS. 22(a) and (b) show schematic explanatory views of an embodiment ofan optical shutter of the present invention, and FIG. 22(a) shows aperspective view thereof and FIG. 22(b) shows a top view thereof.

FIGS. 23(a), (b), and (c) show schematic explanatory views of anotherembodiment of an optical shutter of the present invention, and FIG.23(a) shows a perspective view thereof, FIG. 23(b) shows a top viewthereof, and FIG. 23(c) shows an enlarged view of a shield thereof.

FIG. 24 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 25 shows a schematic perspective view of still another embodimentof a piezoelectric/electrostrictive device of the present invention.

FIG. 26 shows a schematic explanatory view for describing the definitionof a displacement in a piezoelectric/ electrostrictive device of thepresent invention.

FIG. 27 shows a schematic perspective view of an embodiment of aconventional piezoelectric actuator.

FIGS. 28(a) and (b) show a sectional view exemplarily showing adisplacement state of a piezoelectric/electrostrictive device of thepresent invention, and FIG. 28(a) shows a sectional view exemplarilyshowing a state prior to a displacement, and FIG. 28(b) shows asectional view exemparily showing a state after the displacement.

BEST MODE OF CARRYING OUT THE INVENTION

A piezoelectric/electrostrictive device of the present invention ishereinafter described with reference to the drawings. However, thepresent invention is not limited to illustrated embodiments shown in thedrawings.

As exemplarily shown in FIG. 1, a device according to the presentinvention has a mechanism to drive a movable portion substantially inparallel to the X-axis, and in extremely large magnitude as aconventional device of this sort. The reason that a movable portion 4largely operates in a specific direction, in the X-axis direction in thecase of FIG. 1, is that one end of a piezoelectric/electrostrictiveoperating portion 2′ in a direction in which a fixing portion 5 isconnected with the movable portion 4 of a piezoelectric/electrostrictiveelement 2 including the piezoelectric/electrostrictive operating portion2′ comprising a pair of the electrodes and apiezoelectric/electrostrictive layer exists on the fixing portion 5 orthe movable portion 4, and the other end of thepiezoelectric/electrostrictive operating portion 2′ is arranged on thinplate portion 6, at least one end of a piezoelectric/electrostrictivelayer of the piezoelectric/electrostrictive 2 exists on the fixingportion 5 or the movable portion 4, and the other end thereof isarranged on the thin plate portion 6, and the Young's modulus Y1 of amaterial composing the thin plate portions 6 and 7 and the Young'smodulus Y2 of a material composing the piezoelectric/electrostrictivelayer 2 a have a relationship that satisfies the following expression;

1<Y1/Y2≦20.

More particularly, the reason is that, as shown in FIGS. 2(a) and (b),one end of a piezoelectric/electrostrictive element 2 including a pairof electrodes 2 b and 2 c and a piezoelectric/electrostrictive layer 2a, and one end of the piezoelectric operating portion 2′ exist on thefixing portion 5, and the other end of a piezoelectric/electrostrictiveoperating portion 2′ is extended, to be formed, to at least a part ofthe thin plate portions 6 and 7, while the ends of thepiezoelectric/electrostrictive operating portion 2′ of the other endside and of the piezoelectric/electrostrictive layer 2 a are formed tobe within a range not to exceed the entire length of the thin plateportions 6 and 7, and the Young's modulus Y1 of a material composing thethin plate portions 6 and 7 and the Young's modulus Y2 of a materialcomposing the piezoelectric/electrostrictive layer 2 a have arelationship which satisfies the following expression, namely;

1<Y1/Y2≦20.

Without saying, whereas examples of FIGS. 2(a) and (b) are in a modethat one end of a piezoelectric/electrostrictive element 2 including apair of the electrodes 2 b and 2 c and a piezoelectric/electrostrictivelayer 2 a and one end of the piezoelectric/electrostrictive operatingportion 2′ respectively exist on the fixing portion 5, respective endsmay also exist on the movable portion 4.

In other words, in the structure described previously, by making theYoung's modulus of thin plate portions larger than the Young's modulusof a piezoelectric/electrostrictive layer, a displacement of apiezoelectric/electrostrictive element can be effectively converted intoa bending displacement of a driving portion, thus a displacement of amovable portion to be driven by the bending displacement can be madelarger, and the movable portion is facilitated to displace substantiallyin parallel. Contrarily, when the Young's modulus of the thin plateportions is small, not only a displacement of the movable portion ismade smaller, but also a flapping component in the Y-axis direction anda displacement component in the Z-axis direction is increased, thus adisplacement in the rotational mode is made likely to be generated, thusmaking it difficult to have a dominant uniaxial displacement in theX-axis direction. On the other hand, if the Young's modulus of the thinplate portions exceeds twenty times the Young's modulus of thepiezoelectric/electrostrictive layer, the thin plate portions againbecome hard to bend, thus generating a phenomenon that a displacement ofthe movable portion is made smaller, and therefore it is necessary toselect the composition of the material within the range defined by theabove-described expressions.

By the way, it is preferable to structure the above describedpiezoelectric/electrostrictive device such that the movable portiondisplaces in a range that an angle θ formed by a side, opposing to thefixing portion, of the movable portion in a displaced state and the sameside of the movable portion prior to the displacement satisfies thefollowing expression, namely;

0°≦θ≦0.1°.

The displacement of the movable portion in this manner can be obtainednot only by employing the above-described structures for respectivemembers, but also by suitably selecting the Young's modulus for the thinplate portions and the Young's modulus for thepiezoelectric/electrostrictive layer within a range describedpreviously, thus a larger displacement is obtained.

Now, the relationship between the length L of the portion of thepiezoelectric/electrostrictive operating portion 2′ arranged on the thinplate portions 6 and 7, the length e of the thin plate portions 6 and 7,and the thickness d of the thin plate portions 6 and 7, is describedwith reference to FIG. 3. FIG. 3 is for describing the relationshipbetween the length “L” of a piezoelectric operating portion of thepiezoelectric/electrostrictive element 2 arranged on the thin plateportions 6 and 7, the length “e” of the thin plate portions 6 and 7, andthe thickness “d” of the thin plate portions 6 and 7. By arranging thelength L of a portion, on the thin plate portions 6 and 7, of apiezoelectric/electrostrictive operating portion 2′ out of thepiezoelectric/electrostrictive element 2, and the thin plate portions 6and 7 having a specific thickness d and a specific length e so that, outof the piezoelectric/electrostrictive element 2, the length L of theportion of the piezoelectric/electrostrictive operating portion 2′arranged on the thin plate portions 6 and 7, the length e of the thinplate portions 6 and 7, and the thickness d of the thin plate portions 6and 7 satisfies the following expression, namely;

30≦(L/e)×100≦100−d/2.5,

the movement of the piezoelectric/electrostrictive element 2 can besurely transferred to the thin plate portion 6, and the thin plateportions 6 and 7 are efficiently bent, and as a result, it becomespossible to have the movable portion 4 largely displaced substantiallyin parallel. Although, in the mode shown in FIG. 3, one end of thepiezoelectric/electrostrictive operating portion 2′ of thepiezoelectric/electrostrictive element 2 is formed on the fixing portion5, of course, in a device of the present invention, depending on themodes of use, one end of piezoelectric/electrostrictive operatingportion 2′ of the piezoelectric/electrostrictive element 2 may be formedon the movable portion 4.

A piezoelectric/electrostrictive device having an inflection point ofthe displacement on the thin plate portion 6, which is a preferableembodiment of the present invention, is described with reference to FIG.1. In this embodiment, a device is structured so as to satisfy theabove-described expression, namely;

30≦(L/e)×100≦100−d/2.5,

and in a virtual circle having the center thereof on a perpendiculardropped from the middle point of a side, opposing to the fixing portion5, of the movable portion 4, in a non-displacement state, to the fixingpoint 5, and passing through the middle point of the movable portion 4in the non-displacement state and the middle point of the movableportion 4 displaced by operation of the driving portion 3, the movableportion 4 is displaced such that a relationship between the radius r ofthe virtual circle and the length e of the thin plate portion 6satisfies the following expression, namely;

0≦e/r≦100,

and by so structuring that, when the device is driven by a displacementof the piezoelectric/electrostrictive element 2, on the thin plateportion 6 which is bent so as to displace the movable portion 4, theinflection point of the displacement, for the displacement of thebending mode, exists on the thin plate portion, a substantially parallelas well as large displacement is made obtainable. Specifically, thevalue of Y1/Y2 is to be selected within the above-described rangedepending upon the value of (L/e)×100.

In FIG. 1, symbol A denotes the middle point of the movable portion 4 inthe X-axis direction in a state where the device is not driven, andsymbol A′ denotes the middle point of the movable portion 4 in theX-axis direction in a state where the device is driven. A coordinate ofthe middle point A of the movable portion 4 in the X-axis direction in astate where the device is not driven, and a coordinate of the middlepoint A′ of the movable portion 4 in the X-axis direction where thedevice is driven at a predetermined voltage are found, a displacementpath of the movable portion 4 is approximated to a circle passing thetwo points of A and A′, and on an assumption that the center thereofexists on a perpendicular dropped from the point A of the movableportion 4 to the fixing point in a state where the device is not driven,the radius r of the above-described virtual circle is derived. When themovable portion 4 performs such operation that satisfies the followingratio e/r between the radius r thus derived of the virtual circle andthe length e of the thin plate portion 6 in a state where the device isnot driven, the ratio e/r being;

0≦e/r≦100,

a surface of the tip of the movable portion 4 comes to displace insubstantially parallel to a surface of the lower tip of the fixingportion 5, and in a state where a distance between the movable portion 4and the fixing portion 5 is substantially unchanged even during thedisplacement. By doing in this manner, a larger displacement can beobtained. The inflection point at this time ordinarily exists on thethin plate portion 6 in the vicinity of the end ofpiezoelectric/electrostrictive operating portion 2′ arranged on the thinplate portion 6.

A device of another more preferable embodiment is described withreference to FIG. 3. In this embodiment, the length L of a portionarranged on the thin plate portions 6 and 7 out of thepiezoelectric/electrostrictive operating portion 2′ is structured suchthat the relationship between the length e of the thin plate portions 6and 7 and the thickness d of the thin plate portions 6 and 7 satisfiesthe following expression; namely

40≦(L/e)×100≦100−d/1.5

In other words, in the present embodiment, it is shown that bystructuring so as to have the value of (the length L of a portionarranged on the thin plate portions 6 and 7 out of the above-describedpiezoelectric/electrostrictive operating portion 2′/the length e of thethin plate portions 6 and 7) ×100 is 40 or more, in other words, so asto have the length L of the portion arranged on the thin plate portions6 and 7 out of the piezoelectric/electrostrictive operating portion atleast 40% of the length of the thin plate portions 6 and 7, and withregard to the relationship with the thickness d of the thin plateportions 6 and 7, so as to select the thickness d of the thin plateportions 6 and 7 to satisfy ≦100−d/1.5, a substantially paralleldisplacement can be obtained.

FIGS. 2(a) and (b) show a device of still another embodiment. In thisembodiment, a device is structured so as to satisfy the above-describedexpression, namely;

40≦(L/e)×100≦100−d/1.5,

as well as, as to be described hereinafter, to have the inflection pointfor displacement positioned at a position of the thin plate portions 6and 7 parted from a joined portion of the fixing portion 5, where thepiezoelectric/electrostrictive operating portion 2′ exists, or themovable portion 4 and the thin plate portions 6 and 7 by one half ormore of the length of the thin plate portions 6 and 7, and in a virtualcircle having the center thereof on a perpendicular dropped to thefixing portion 5, from the middle point of one side, opposing the fixingportion 5, of the movable portion 4 in a non-displacement state of thedevice, and passing through the middle point of the movable portion 4 inthe non-displacement state, and the middle point of the movable portiondisplaced by operation of the driving portion 3, the movable portion 4is displaced such that a relationship between the radius r of thevirtual circle and the length e of the thin plate portions 6 and 7satisfies the following expression, namely;

0≦e/r≦20.

In order to have the operation such that a relationship between theradius r of the virtual circle and the length e of the thin plateportions 6 and 7 satisfies the following expression, namely;

0≦e/r≦20,

the value of Y1/Y2 is to be suitably selected within the above-describedrange depending on the value of (L/e)×100, in order that there exists arelationship which satisfies Li/e≧0.5 between the length of the thinplate portions 6 and 7 indicated by the symbol “e” in FIG. 2(a) and thedistance from a joined portion of the thin plate portions 6 and 7 to aninflection point indicated by the symbol “Li” in FIG. 2(b) with thefixing portion 5. By this structure, a larger displacement is madeobtainable, while driving force is made stronger, as the structure isadvantageous to the displacement, namely having a structure whereoperation relative to the X-axis is facilitated.

1. Embodiment of the Device

Now, a representative example of a device according to the presentinvention is described with reference to FIG. 4 to FIG. 6. A deviceshown in FIG. 4 is first described. In an embodiment shown in FIG. 4, afirst electrode 2 c is firstly formed from a position close to an end ofthe fixing portion 5 toward the movable portion 4, within a range notexceeding the entire length of the thin plate portions 6 and 7, so as tocover the thin plate portions 6 and 7. Then, thereover, apiezoelectric/electrostrictive layer 2 a is formed from a position ofmore or less middle of the fixing portion 5 toward the movable portion4, within a range not exceeding the entire length of the thin plateportions 6 and 7, so as to completely cover the above-described firstelectrode 2 c. Then, thereover, a second electrode 2 b is formed so thatone end thereof is positioned close to an end of thepiezoelectric/electrostrictive layer 2 a formed on the fixing portion 5and the other end thereof positioned on the thin plate portions 6 and 7is positioned at the same position as the first electrode 2 c. Further,over the first electrode 2 c and the second electrode 2 b existing onthe fixing portion 5, terminal electrodes 10 are respectively formed.

Thus fabricated is a device having a structure where one end of apiezoelectric/electrostrictive operating portion 2′ comprising a pair ofor more electrodes 2 b and 2 c and a piezoelectric/electrostrictivelayer 2 a in a direction in which the fixing portion 5 is connected withthe movable portion 4 exists on the fixing portion 5, the other end sideof the piezoelectric/electrostrictive operating portion 2′ is extended,to be formed, to at least a portion of the thin plate portions 6 and 7,and ends of the piezoelectric/electro-strictive operating portion 2′ ofthe other end side and of the piezoelectric/electrostrictive layer 2 aare arranged to be within a range not exceeding the entire length of thethin plate portions 6 and 7. By arranging in this manner, apiezoelectric/electrostrictive layer is constituted to be longer thanthe second electrode 2 b, thus a short circuit of the second electrode 2b with the first electrode 2 c can be effectively prevented, andconnection of terminals with outside leads can be fabricated with higheryield. In this embodiment, a yttrium oxide partially-stabilized zirconiamaterial having a Young's modulus Y1 of 200 GPa is used as a materialcomposing the thin plate portions 6 and 7, lead zirconate-leadtitanate-lead magnesium niobate solid solution having a Young's modulusY2 of 60 GPa is used for a piezoelectric/electrostrictive layer 2 a, andthe ratio of the both Young's moduli is set to be 3.33 which is thevalue that satisfies the following expression, namely;

1<Y1/Y2≦20.

By such structure, the movable portion 4 can be made to displacesubstantially parallel relative to the fixing portion 5. Further, theangle q formed by a side, opposing to the fixing portion, of the movableportion in a displaced state and the same side of the movable portionprior to the displacement is found to be 0.05°, the value whichsatisfies the following expression, namely;

0°≦θ≦0.1°.

Moreover, in an embodiment shown in FIG. 5, an example is shown in whicha piezoelectric/electrostrictive element has a first electrode 2 cformed longer than a piezoelectric/electrostrictive layer 2 a and asecond electrode 2 b, namely formed closer to the movable portion 4. Bythis structure, in the embodiment, different from the embodiment shownin FIG. 4, a portion where a piezoelectric/electrostrictive layer 2 adirectly touches the thin plate portions 6 and 7 ceases to exist, andthe piezoelectric/electrostrictive layer 2 a is made to be joined withthe thin plate portions 6 and 7 via a first electrode 2 c, which ispreferable from a viewpoint of adhesive property. An end of apiezoelectric/electrostrictive operating portion 2′ comprising a pair ofelectrodes 2 b and 2 c and a piezoelectric/electrostrictive layer 2 a isformed to be positioned at around 75% distance, from a joined portion ofthe fixing portion 5 with the thin plate portions 6 and 7, relative tothe length of the thin plate portions 6 and 7. Of course, the Young'smodulus Y1 of a material of the thin plate portions 6 and 7, and theYoung's modulus Y2 of a material for the piezoelectric/electrostrictivelayer 2 a are respectively selected to satisfy the following expression,namely;

1<Y1/Y2≦20

Further, in this example, terminals 11 for connecting with electriccircuits or the like of the outside are formed on the movable portion 4and the fixing portion 5. Consequently, a variety of sensors, a magnetichead, a slider mounted with a magnetic head or the like can be directlymounted on the movable portion 4 without use of a lead. The terminals 11of the fixing portion 5 have continuity with respective terminals 11 ofthe movable portion 4 through wiring 12 formed on the surfaces oppositeto the surfaces of the thin plate portions 6 and 7 where thepiezoelectric/electrostrictive elements 2 are arranged and inner wiringof the movable portion 4 and the fixing portion 5 so as to be mutuallyone to one.

By forming, for example, a device shown in FIG. 5 such that the length L(not shown) of a portion arranged on the thin plate portions 6 and 7 outof the piezoelectric/electrostrictive operating portion 2′, relative toa relationship between the length e of the thin plate portions 6 and 7and the thickness d of the thin plate portions 6 and 7, satisfies thefollowing expression, namely;

30≦(L/e)×100≦100−d/2.5

operation of the piezoelectric/electrostrictive element 2 can bereliably transferred to the thin plate portions 6 and 7, and can havethe thin plate portions 6 and 7 efficiently bent, and as the result, apiezoelectric/electrostrictive device, capable of largely displacing themovable portion 4 substantially in parallel, can be can be provided.

It should be noted that, in the above described embodiment, bystructuring the device such that an inflection point for a displacementexists on the thin plate portion 6, when the device is driven by thedisplacement of the piezoelectric/electrostrictive element 2, and suchthat the movable portion 4 displaces so that a relationship between theradius r of the virtual circle and the length e of the thin plateportion 6 satisfies the following expression, in a virtual circle havingthe center thereof on a perpendicular dropped to the fixing portion 5from the middle point of a side, opposing to the fixing portion 5, ofthe movable portion 4 in non-displacement state, and passing through themiddle point of the movable portion 4 in the non-displacement state andthe middle point of the movable portion 4 displaced by operation of thedriving portion 3, the expression being;

0≦e/r≦100,

a piezoelectric/electrostrictive device capable of largely displacingthe movable portion 4 more effectively and substantially in parallel canbe obtained. And in order to ensure the displacement mode, the value ofY1/Y2 may be suitably selected within the range described above,depending on the value of (L/e)×100.

By this structure, while increasing the driving force, an advantageousstructure for the displacement, namely a structure facilitating amovement relative to the X-axis is obtained, thus a larger displacementcan be obtained. In a device structured to have such a relationship, thethin plate portions have a portion where stiffness, which is determinedby a specified length and by the ratio of the Young's moduli Y1/Y2, isrelatively low. And when the movable portion is displaced by thedisplacement of a piezoelectric/electrostrictive element, the portionwhere the stiffness, which is determined by the length and the materialproperty thereof, is low makes the deformation of the thin plateportions to be unique, enabling the movable portion to displacesubstantially in parallel and in larger magnitude.

Moreover, if the length L of a portion arranged on the thin plateportions 6 and 7 out of the piezoelectric/ electrostrictive operatingportion 2′ , the length e of the thin plate portions 6 and 7, and thethickness d of the thin plate portions 6 and 7 are selected so as tosatisfy the following expression, namely;

40≦(L/e)×100≦100−d/1.5,

specifically, in a virtual circle, having the center thereof on aperpendicular dropped to the fixing portion 5 from the middle point of aside, opposing the fixing point 5, of the movable portion 4 innon-displacement state, and passing through the middle point of themovable portion 4 in the non-displacement state and the middle point ofthe movable portion 4 displaced by operation of the driving portion 3,the movable portion 4 displaces such that a relationship between theradius r of the virtual circle and the length e of the thin plateportions 6 and 7 satisfies the following expression, namely;

0≦e/r≦20,

and the value Y1/Y2 is suitably selected within the above-describedrange depending on the value of (L/e)×100, so that an inflection pointof a displacement exists at a position on the thin plate portions 6 and7 parted by one half or more of the length of the thin plate portionfrom a joined portion, with the thin plate portions 6 and 7, of thefixing portion 5 or the movable portion 4 to the thin plate portions 6and 7; the piezoelectric/electrostrictive operating portion 2′ existingon either a position of the fixing portion or the movable portion, thusthe movable portion,4 can be displaced substantially in parallel and inlarger magnitude.

An embodiment shown in FIG. 6 shows an example where the lengths of themovable portion 4 and the fixing portion 5 are made shorter, and thewidths of the thin plate portions 6 and 7 are made equivalent with thethickness of the device. According to the embodiment, the bottomsurfaces and the upper surfaces, which are substantially square, of thefixing portion 5 and the movable portion 4 are made to be surfaces forbonding with the substrate and other members, and the surfaces forbonding are made to be mutually displaced substantially in parallel. Byutilizing such an embodiment, one may have a wider area for bonding, orone may preferably use it, as a part for hard disks, for a mechanism ina precise positioning of heads by installing a suspension mounted with aslider on the movable portion 4 side, and installing a carriage arm onthe fixing portion 5 side.

In other words, as the fixing portion 5 and the movable portion 4 can bemoved as if in sheared shape, the structure is that can utilize a largerdisplacement, in comparison with a case where a displacement is operatedby use of the d15 shear mode of a piezoelectric material bulk. Inimplementing such a device according to FIG. 6, it is preferable to havea ratio e/a of the thickness a of the hole 8 and the length e of thethin plate portions 6 and 7 at 0.1 to 2, and a ratio afb of thethickness a of the hole 8 and the width b of the thin plate portions 6and 7 at 0.05 to 2. The defined value of the e/a is important inincreasing the paralleling degree of mutual displacements of theabove-described bonding surfaces, while the defined value of the a/b isimportant in increasing a driving force of the driving portion 3 anddisplacement components in a direction of a specific axis, in this casethe X-axis.

FIGS. 7(a), (b), and (c) show explanatory views of a structure of apiezoelectric/electrostrictive operating portion 2′, and therefore, inthe drawings, out of a pair of thin plate portions 6 and 7, only a thinplate portion 6 having at least a piezoelectric/electrostrictive element2 formed thereon is shown. FIGS. 7(a), (b), and (c) show exemplary viewsshowing mutual relationship between a second electrode 2 b, a firstelectrode 2 c, and a piezoelectric/electrostrictive layer 2 arespectively constituting a piezoelectric/electrostrictive operatingportion 2′ according to the present invention. FIG. 7(a) exemplarilyshows an embodiment where the second electrode 2 b is arranged in adirection from the fixing portion 5 side toward the movable portion 4exceeding the entire length of the thin plate portion 6, and is formedas if to cover the piezoelectric/electrostrictive layer 2 a and thefirst electrode 2 c, however, the piezoelectric/electrostrictive layer 2a and the first electrode 2 c are arranged respectively with a desireddistance from the movable portion 4, thus the other end of thepiezoelectric/electrostrictive layer 2 a of thepiezoelectric/electrostrictive element 2 is arranged lest it shouldcovers the entire length of the thin plate portion 6. In other words, inthis embodiment, the other end of the piezoelectric/electrostrictiveoperating portion 2′ comprising a pair of electrodes 2 b and 2 c and apiezoelectric/electrostrictive layer 2 a is arranged to be a desiredposition on the thin plate portion 6.

FIG. 7(b) shows an embodiment in an exemplary view where a firstelectrode 2 c is arranged extending from the fixing portion 5 side to apart of the movable portion 4 covering the entire length of the thinplate portion 6, while having a piezoelectric/electrostrictive layer 2 aand a second electrode 2 b arranged thereon with a desired distance fromthe movable portion 4 and in the same length, and also in theembodiment, the other end of the piezoelectric/electrostrictive layer 2a of the piezoelectric/electrostrictive element 2 exists on the thinplate portion 6 and is arranged lest the entire length of thin plateportion 6 should be covered. FIG. 7(c) shows an embodiment where a firstelectrode 2 c and a second electrode 2 b are arranged in the same lengthinterposing a piezoelectric/electrostrictive 2 a, and also in theembodiment, the other end of the piezoelectric/electrostrictive layer 2a of a piezoelectric/electrostrictive element 2 exists on the thin plateportion 6, and is arranged lest the entire length of the thin plateportion 6 should be covered. Of course, the other end of thepiezoelectric/electrostrictive operating portion 2′ comprising a pair ofelectrodes 2 b and 2 c and a piezoelectric/electrostrictive layer 2 a isarranged with a desired distance from the movable portion 4. In thepresent invention, the other end of the piezoelectric/electrostrictiveoperating portion 2′ comprising a pair of electrodes 2 b and 2 c and thepiezoelectric/electrostrictive layer 2 a is arranged with a desireddistance from the movable portion 4 so as to be arranged at a desiredposition on the thin plate portion 6, with the other end of thepiezoelectric/electrostrictive layer 2 a arranged also on the thin plateportion 6. Of course, mutual positional relationship of the secondelectrode 2 b, a piezoelectric/electrostrictive layer 2 a, and the firstelectrode 2 c can take a variety of modes so long as the above-describedrequirements are met.

As can be apparent from the above description, it is preferable toconstitute a piezoelectric/electrostrictive element so that a desiredpart of a driving portion 3 can display enough flexibility. In order tosecure enough flexibility which permits a movable portion 4 to drive“substantially in parallel”, it is necessary that at least thearrangement of the piezoelectric/electrostrictive element arranged onthe thin plate portion 6 is to be made the structure as described above,and a material composing the thin plate portion 6 of which Young'smodulus being Y1 and a material composing thepiezoelectric/electrostrictive layer 2 a of which Young's modulus beingY2 are to be selected so as to satisfy the following expression, namely;

1<Y1/Y2≦20.

To achieve this target, it is necessary to pay enough consideration tothe balance of the thickness of the above-described three members, andthe thickness is preferably 2 to 100 μm for the thin plate portions 6and 7, 0.1 to 50 μm for the electrodes 2 b and 2 c, and 3 to 300 μm forthe piezoelectric/electrostrictive layer 2 a.

Although partially overlapping, FIG. 8 shows a schematic explanatoryview for describing mutual relationship of respective members of adevice according to the present invention. A device 1 comprisesrespective members of a driving portion 3 to be driven by a displacementof a piezoelectric/electrostrictive element 2, a movable portion 4 to bedisplaced based on the drive of the driving portion 3, and a fixingportion 5 for holding the driving portion 3 and the movable portion 4.The driving portion 3 comprises a pair of mutually opposing thin plateportions 6 and 7, and a film-like piezoelectric/electrostrictive element2 formed on the outer surfaces of the thin plate portions 6 and 7, thefixing portion 5 and the movable portion 4 are combined via the drivingportion 3, a piezoelectric/electrostrictive operating portions 2′ existson portions of the thin plate portions 6 and 7 and the fixing portion 5,and a hole 8 is formed by inner walls of the driving portion, an innerwall of the movable portion, and an inner wall of the fixing portion. Insuch a structure where the piezoelectric/electrostrictive operatingportion 2′ extends over the fixing portion 5, a displacement mode of thedriving portion 3 takes a bending displacement mode in which the thinplate portions face toward the outer space, as shown in FIGS. 28(a) and(b), thus the device can have a feature of having the displacementmechanism to largely displace the movable portion 4. In order to ensurethe displacement mode, it is preferable that the distance thepiezoelectric/electrostrictive operating portion 2′ extends over thefixing portion 5 or the movable portion 4 is made to be one half or moreof the thickness d of the thin plate.

Then, the device, relative to the thickness of the hole 8, namely adistance a in the X-axis direction in the drawing, and the width of thethin plate portion, namely a distance b in the Y-axis direction in thedrawing, is structured to have the ratio a/b at 0.5 to 20. Preferably,the ratio a/b is 1 to 10, and more preferably 2 to 8. The defined valueof a/b is based on a finding that a displacement of apiezoelectric/electrostrictive device according to the presentapplication can be made larger and a displacement in the X-Z plane inthe drawing can be dominantly obtained.

On the other hand, relative to the length of the thin plate portions 6and 7, namely a distance e in the Z-axis direction in the drawing andthe thickness a of the above-described hole 8, the ratio e/a ispreferably 0.5 to 10, and more preferably 0.7 to 5.

The defined value of e/a is based on a finding that apiezoelectric/electrostrictive device according to the presentapplication can generate a high displacement at high resonant frequency,namely in a high speed of response. Accordingly, from comprehensiveviewpoint of generated displacement quantity, displacement mode, andresponsibility, if the a/b is set at 0.5 to 20, and the e/a is setwithin 0.5 to 10, more preferably the a/b at 1 to 10, and the e/a within0.7 to 5, there is attained actually a device capable of showing a largedisplacement with relatively low driving voltage and showing suppressedflapped displacement or suppressed vibrations in the Y-axis direction,and having superior in high speed responsibility. This is extremelypreferable.

In a device according to FIG. 6, where the hole 8 has the thickness aand the thin plate portions 6 and 7 have the length e, it is preferableto have the ratio e/a at 0.1 to 2, where the hole 8 has the thickness aand the thin plate portions 6 and 7 have the thickness b, it ispreferable to have the ratio a/b at 0.05 to 2. The defined value of e/ahas an important meaning in increasing the above-described parallelingdegree of the displacement of the joined surfaces, and in increasingresonant frequency, without remarkably decreasing the displacement,while the defined value of a/b has an important meaning in increasingdriving force of the driving portion 3, and in increasing displacementcomponents toward a specific axis of the movable portion 4, for example,in this case, increasing displacement components in the X-axisdirection. In a piezoelectric/electrostrictive device according to thepresent invention, the hole 8 may be filled with a gel material, forexample, silicone gel.

The length f of a movable portion 4 shown in FIG. 8 is preferablyshorter. By shortening, lightening of the weight and increase inresonant frequency can be realized. However, in order to securestiffness of the movable portion 4 toward the X-axis direction, and toensure the displacement, the ratio f/d relative to the thickness d ofthe thin plate portions is set to be 3 or more, and preferably 10 ormore. Actual dimensions of respective members are determined consideringa bonding area for mounting members on the movable portion 4, a bondingarea for mounting the fixing portion 5 on another member, a bonding areafor mounting electrode terminals and the like, mechanical strength anddurability of the device as the entirety, required displacement andresonant frequency, driving voltage, and the like. Ordinarily, a ispreferably to be 100 to 2000 μm, and more preferably 200 to 1000 μm.Ordinarily, b is preferably to be 50 to 2000 μm, and more preferably 100to 500 μm. Ordinarily, d is, relative to the width b of the thin plateportion, made to be b>d, in order that a flapped displacement or adisplacement component in the Y-axis direction can be effectivelysuppressed, and is preferably to be 2 to 100 μm, and more preferably 4to 50 μm.

Ordinarily, e is preferably to be 200 to 3000 μm, and more preferably300 to 2000 μm. And ordinarily, f is preferably 50 to 2000 μm, and morepreferably 100 to 1000 μm. It should be noted that by structuring inthis manner, the ratio of the displacement in the Y-axis directionrelative to the displacement in the X-axis or the major axis directionordinarily does not exceed 10%, however, a low voltage driving can befacilitated by suitably adjusting within a range of the above-mentionedsuitable dimension ratios and the actual dimensions, and thedisplacement component in the Y-axis can be adjusted to be 5% or less,which is an extremely advantageous effect. In other words, asubstantially dominant displacement for the X-axis, or the major axis ismade obtainable. Resultantly, a piezoelectric/electrostrictive devicewhich is superior in high speed responsibility, and capable ofgenerating a large displacement with relatively low voltage, in additionto the above-described features, can be obtained. Moreover, if a deviceis structured to follow the structure shown in FIG. 6, though adisplacement is relatively smaller, a displacement component toward theY-axis can become adjustable even to 3% or less.

Furthermore, in a device 1, the shape of the device is, instead ofboard-like body as shown in FIG. 27 as a conventional example, threedimensional solid shape, for example rectangular, for the movableportion 4 and the fixing portion 5, and as the thin plate portions 6 and7 are straddled so as to have the sides of the movable portion 4 and thefixing portion 5 to be continuous, the stiffness in the Y-axis directionof the device can be selectively increased. In other words, in thedevice 1, the operation of the movable portion 4 only in a planeincluding the driving direction of the driving portion 3, namely in theX-Z plane, can be selectively generated, and the operation of themovable portion 4 in the Y-Z plane, namely the operation in theso-called flapping direction can be suppressed.

A shape of the hole 8 to be formed by inner walls of the driving portion3, an inner wall of the movable portion 4, and an inner wall of thefixing portion can be optional so long as there is no obstruction causedto the operation of the driving portion. In other words, a sectionalview of the hole 8 may be other than rectangular, such as circular,elliptical, trapezoid, parallelogram, or the like.

Now, another embodiment of a piezoelectric/electrostrictive deviceaccording to the present invention is described. FIG. 9 shows a devicehaving one each piezoelectric/electrostrictive element 2 on both plateportions of the pair of thin plate portions 6 and 7, first electrodes 2c of two piezoelectric/electrostrictive elements 2 are made for commonuse, and are drawn out from the fixing portion 5 side of one of thesurfaces where the hole 8 is apertured, and second electrodes 2 b aredirectly drawn out to the fixing portion 5 side of surfaces whererespective piezoelectric/electro-strictive elements are formed. Though,as shown in FIG. 4 to FIG. 6, and FIG. 8 and FIG. 9, apiezoelectric/electrostrictive element 2 formed on at least a part ofthe outer surface of at least one of thin plate portions 6 or 7 of thethin plate portions 6 and 7, has a width the same as the width of thinplate portions 6 and 7, of course, one narrower than the width of thethin plate portions 6 and 7 may be used. However, the width of thepiezoelectric/electrostrictive element 2 is preferably the same as thewidth of the thin plate portions 6 and 7, as this serves to increase thedriving force of the driving portion 3, and to favorably act on thehigher displacement.

FIG. 10 and FIG. 11 show, different from the above-described FIG. 9,examples where one end of a piezoelectric/electrostrictive operatingportion 2′ comprising a pair of electrodes and apiezoelectric/electrostrictive layer is arranged on a movable portion 4,the other end of the piezoelectric/electrostrictive operating portion 2′is extended, to be formed, to at least a part of the thin plate portions6 and 7, and ends of the piezoelectric/electrostrictive operatingportion 2′ and a piezoelectric/electrostrictive layer on the other endside are formed within a range not exceeding the entire length of thethin plate portions 6 and 7. In other words, in FIG. 9, thepiezoelectric/electrostrictive operating portion 2′ is formed in a modeextending to the thin plate portions 6 and 7 and the fixing portion 5,while in FIG. 10 and FIG. 11, the piezoelectric/electrostrictiveoperating portion 2′ is formed contrarily in a mode extending to thethin plate portions 6 and 7 and the movable portion 4. In FIG. 10 andFIG. 11, in the same way as in FIG. 9, the width of thepiezoelectric/electrostrictive element 2 is also made to be the same asthe width of the thin plate portions 6 and 7, thus the same effect canbe obtained as the device shown in FIG. 9, and in addition, the movableportion 4 per se can be displaced basically in the same way as thedevice shown in FIG. 9.

Now, arrangement of driving signal applying terminals shown in FIG. 12and FIG. 13 is described. Respectively in both examples, one end of apiezoelectric/electrostrictive operating portion 2′ comprising a pair ofelectrodes and a piezoelectric/electrostrictive layer 2 a exists on afixing portion 5, the other end side of thepiezoelectric/electrostrictive layer 2′ is extended, to be formed, atleast to a part of the thin plate portions 6 and 7, and ends of apiezoelectric/electrostrictive operating portion 2′ andpiezoelectric/electrostrictive layers of the other end side exist on thethin plate portions 6 and 7, and are formed to be in a range notexceeding the entire length thereof. FIG. 12 shows an example where thedriving signal applying terminals 10 are arranged on a side of thefixing plate 5, namely on the same surface as a surface where thepiezoelectric/electrostrictive element 2 is formed, basically similarlywith the case shown in FIG. 4. According to the structure, a device canbe fixed independently of the surface where the terminals are arranged,and as the result, high reliability can be attained for fixing of thedevice and bonding between circuits and terminals.

It should be noted, in the embodiment, that terminals and circuits arebonded by means of the flexible print circuit (also called FPC), theflexible flat cable (also called FFC), the wire bonding, or the like.FIG. 13 shows driving signal applying terminals 10 arranged on a surfacewhich orthogonally crosses a surface where apiezoelectric/electrostrictive element 2 is arranged. If the surfacewhere the driving signal applying terminals 10 are formed is utilized asa fixing surface, connecting of the driving signal applying terminals 10with circuits (not shown) and fixing of the device per se can besimultaneously performed, which is an advantage in facilitatingcompaction of an apparatus per se. Of course, a device may be fixed onan opposite surface 9 which is unformed of the driving signal applyingterminals. In this embodiment, through-holes are formed in advance onthe fixing portion 5, and after the through-holes are filled with aconductive material, a pattern of the piezoelectric/electrostrictiveelement 2 is formed so as to have respective electrodes bonded with thethrough-holes, and then the filled surfaces of the through-holes areexposed by machining, thus the surfaces are utilized as the drivingsignal applying terminals 10. As the conductive material, a lead may beembedded. In this example, a through-hole provided in the vicinity ofthe hole 8 is used as a common terminal.

In addition to the above-described advantages, a device of the presentinvention has an advantage that, as for members except for apiezoelectric/electrostrictive element 2, a suitable composing materialcan be selected depending on the required properties of respectivemembers, as the entirety is not necessarily required to be composed of apiezoelectric/electrostrictive material. In other words, by composingthe members except for the piezoelectric/electrostrictive element 2 witha material of lighter weight, the device can be made to be scarcelyinfluenced by harmful vibrations in operation, and in the similarmanner, improvement in the mechanical strength, handling property,impact resistance, and humidity resistance can be facilitated.

Further, as the use of a filler is not required, the efficiency of thedisplacement due to the inverse piezoelectric effect and theelectrostrictive effect is never deteriorated. 2. Constituting Elementsof the Device

Now, though partially repeating the description so far made, respectivemembers constituting a device of the present invention are individuallyand specifically described with an example of the device 1 shown in FIG.8.

(1) Movable Portion and Fixing Portion

A movable portion 4 is a portion to be operated based on the drivingquantity of the driving portion 3, and a variety of members are mountedthereon depending on application uses. For example, when a device 1 isused as a displacement element, members requiring positioning aremounted, such as a shield for an optical shutter, a magnetic head, aslider with a magnetic head mounted thereon, a suspension with a slidermounted thereon, or the like, for positioning a hard disk or ringingsuppression mechanism.

A fixing portion 5 is a portion for holding the driving portion 3 andthe movable portion 4, and by holding and securing the fixing portion 5to any substrate, for example, a carriage arm fixed to a VCM (voice coilmotor), either a fixing plate or a suspension fixed to said carriagearm, and the like, when utilizing it for positioning the above-describedhard disk, the device 1 as an entirety is secured.

Further, electrode leads or other members may also be arranged in orderto control a piezoelectric/electrostrictive element 2. As a materialcomposing the movable portion 4 and the fixing portion 5, there is nolimitation so long as stiffness exists therein, however, a ceramic, towhich the ceramic green sheet laminating method, to be hereinafterdescribed, is applicable, can be preferably used. The ceramic includes amaterial, particularly, containing zirconia, such as fully-stabilizedzirconia, partially-stabilized zirconia, or the like, alumina, magnesia,silicon nitride, aluminum nitride, or titanium oxide as the majorcomponent, and in addition thereto, a material containing mixturethereof as the major component may also be used, however, in points ofhigh mechanical strength and high toughness, zirconia, specifically amaterial containing fully-stabilized zirconia as the major component ora material containing partially stabilized zirconia as the majorcomponent is preferable. The major component means a component containedin a material in 50 or more mass (weight) %. Further, instead of theceramic, a metal can also be used in the composition.

(2) Driving Portion

A driving portion 3 is a portion to be driven by a displacement of apiezoelectric/electrostrictive element 2, comprising mutually opposingthin plate portions 6 and 7, and a film-likepiezoelectric/electrostrictive element 2 formed on the surface of thethin plate portions 6 and 7.

{circle around (1)} Thin Plate Portions

Thin plate portions 6 and 7 are thin-plate-like members havingflexibility, and have a function of amplifying an expanding orcontracting displacement of a piezoelectric/electrostrictive element 2arranged on the surface thereof into a bending displacement, to transmitto a movable portion 4.

Accordingly, a figure or a material of the thin plate portions 6 and 7is sufficed if a material composing the thin plate portions having theYoung's modulus Y1 and a material composing thepiezoelectric/electrostrictive layer having the Young's modulus Y2 havea relationship therebetween that satisfies the following expression,namely;

1<Y1/Y2≦20,

have flexibility as a matter of course, and have mechanical strength inan order of being unbreakable by a bending deformation, and thematerials can be suitably selected from a ceramic, a metal, or the like,similarly with the above-described movable portion and fixing portion,within a range that satisfies the relationship of the Young's moduli,considering responsibility and operability of the movable portion.

Ordinarily, the thickness of the thin plate portions 6 and 7 ispreferably around 2 to 100 μm, combined thickness of the thin plateportion 6 or 7 and a piezoelectric/electrostrictive element 2 ispreferably 7 to 500 μm. Further, in the structure of a device accordingto the present invention, in order to further improve targeted effects,the thickness of electrodes 2 b and 2 c are preferably made to be 0.1 to50 μm, and the thickness of a piezoelectric/electrostrictive layer 2 ais preferably made to be 3 to 300 μm, considering the above-describedrelationship between the Young's modulus of the material of the thinplate portions and the Young's modulus of the material ofpiezoelectric/electrostrictive layer. Further, the width of the thinplate portions 6 and 7 is preferably 50 to 2000 μm. As a materialcomposing the thin plate portions 6 and 7, a ceramic similar to the sameused for the movable portion 4 and the fixing portion 5 can bepreferably used, and zirconia, specifically a material containingfully-stabilized zirconia as the major component or a materialcontaining partially-stabilized zirconia as the major component can bemost preferably employed because of its high mechanical strength whenmade into a thin body, high toughness, and small reactivity with apiezoelectric/electrostrictive layer or an electrode material. As forfully-stabilized or partially-stabilized zirconia, preferable is thesame stabilized in the following way. Although zirconia can be partiallyor fully stabilized by adding or containing at least any one of oxidessuch as yttrium oxide, ytterbium oxide, cerium oxide, calcium oxide, andmagnesium oxide, targeted stabilization of zirconia is possible not onlyby adding one kind out of the above listed compounds, but also by addingcombination of the compounds.

It should be noted that a load of respective compounds is 1 to 30 mol %(mole percent), preferably 1.5 to 10 mol % for yttrium oxide orytterbium oxide, 6 to 50 mol %, preferably 8 to 20 mol % for ceriumoxide, 5 to 40 mol %, preferably 5 to 20 mol % for calcium oxide ormagnesium oxide, and among these, specifically preferable for thestabilizer is yttrium oxide, and in the case, the load is preferably 1.5to 10 mol %, and more preferably 2 to 4 mol %. Further, as aco-sintering agent or the like, alumina, silica, magnesia, transitionmetal oxide, or the like can also be added within a range of 0.05 to 20wt % (weight percent), however, when the sintering integration by thefilm forming method is employed as the formation method of apiezoelectric/electrostrictive element, alumina, magnesia, transitionmetal oxide, or the like may be preferably added as an additive.

In order that the above-described mechanical strength and the stabilizedcrystal phase may be obtained, it is preferable to have zirconia havinga mean crystal grain diameter of 0.05 to 3 μm, preferably 0.05 to 1 μmor less. As for the thin plate portions 6 and 7, as describedpreviously, a ceramic, similar to the same used for the movable portionand the fixing portion, may be used, however, it is preferable tocompose using substantially the same material in view of improvedreliability of the joined portions, higher mechanical strength of thedevice, and reduction of the complication in fabrication.

{circle around (2)} Piezoelectric/Electrostrictive Element

A piezoelectric/electrostrictive element 2 at least comprises apiezoelectric/electrostrictive layer and a pair of or more electrodesfor applying a voltage to the piezoelectric/electrostrictive layer.Although a conventionally known piezoelectric/electrostrictive element 2of unimorph-type, bimorph-type, or the like may be used, it ispreferable to constitute a device described in the present applicationwith a piezoelectric/electrostrictive element 2 of unimorph-type, as theunimorph-type is superior in stability of the displacement quantity tobe generated, and advantageous in lightening the weight thereof. Forexample, as shown in FIG. 14, a laminated-typepiezoelectric/electrostrictive element 2 or the like having a firstelectrode 2 c, a piezoelectric/electrostrictive layer 2 a, and a secondelectrode 2 b laminated in layers can be preferably used. When apiezoelectric material such as ferroelectric substance or the like isordinarily used for a piezoelectric/electrostrictive layer, if a voltageis applied across the above-described electrodes (for example, betweenthe second electrode 2 b and the first electrode 2 c) to cause anelectric field to operate on the piezoelectric/electrostrictive layer 2,based on the electric field, an electric field induced distortion isinduced to the piezoelectric/electrostrictive layer 2, and apiezoelectric/electrostrictive element described in FIG. 14 has afunction, as a lateral effect of the electric field induced distortion,of mainly generating a distortion in the contracting mode in a directionparallel to the main surface of the piezoelectric/electrostrictive layer2. Accordingly, if the piezoelectric/electrostrictive element 2 of thestructure is applied to a device of the present invention, theabove-described distortion which contracts in a direction of the mainsurface described previously is converted into a bending displacementfor bending the thin plate portions 6 and 7, and the driving portion 3is bent and displaced having the joined portion of the thin plateportions 6 and 7 with the movable portion 4 or of the thin plateportions 6 and 7 with the fixing portion 5 as the fulcrums in adirection toward the outer space (opposite direction of the hole), andas the result, the movable portion can be displaced in a predetermineddirection.

Further, a piezoelectric/electrostrictive element 2 may also bepreferably structured such that, in addition to the structure where thepiezoelectric/electrostrictive layer 2 a is interposed by a pair ofupper and lower electrodes, a piezoelectric/electrostrictive layer 2 ais further formed on the second electrode, a third electrode is furtherformed on the piezoelectric/electrostrictive layer 2 a, thus having twolayers of piezoelectric/electrostrictive operating portion 2′.Furthermore, it is also preferable to have a structure in thatelectrodes 2 b and 2 c, and a piezoelectric/electrostrictive layer 2 aare repeatedly laminated, thus having the piezoelectric/electrostrictiveoperating portions in three layers, four layers, five layers, or evenmore. By thus making the piezoelectric/electrostrictive operatingportions 2′ in multi-layered structure, driving force of the drivingportion can be increased, a displacement can be made larger, stiffnessof the device per se can be increased, thus realizing higher resonantfrequency and high speed responsibility. Moreover, in a structure wherestiffness of the device per se is increased, for example, in a structurewhere thickness of the thin plate portions is thickened, a largerdisplacement and higher resonant frequency can be facilitated with ease.

For example, a piezoelectric/electrostrictive element 2 shown in FIG. 24has piezoelectric/electrostrictive operating portions 2′ in two layers.Respective piezoelectric/electrostrictive elements 2 have the elementstructure shown in FIG. 14, where a first electrode 2 c, apiezoelectric/electrostrictive layer 2 a, a second electrode 2 b, apiezoelectric/electrostrictive layer 2 a, and a first electrode 2 c aresequentially laminated, and the piezoelectric/electrostrictive operatingportion comprising a pair of electrodes 2 b and 2 c and apiezoelectric/electrostrictive 2 a are formed in two layers in alaminating direction of the composing films of the element. Further,electrodes in the same element and denoted by the same symbol arerespectively applied by a voltage of the same potential, and terminalsfor causing an electric current to flow to respective electrode are allformed on a surface of the fixing portion 5 where elements are formed.Furthermore, though the device shown in FIG. 24 shows an embodimentwhere a first electrode 2 c is made for common use by apiezoelectric/electrostrictive operating portion of the first layer anda piezoelectric/electrostrictive operating portion of the second layer,these maybe, of course, independent electrode structure. Naturally, oneend of the piezoelectric/electrostrictive operating portion exists onthe fixing portion 5, and the other end is arranged on the thin plateportions 6 and 7, and other end of the piezoelectric/electrostrictivelayer 2 a exists on the thin plate portions 6 and 7, and is arranged tobe within a range not exceeding the entire length of the thin plateportions. A piezoelectric/electrostrictive element 2 shown in FIG. 25has a piezoelectric/electrostrictive operating portion in three layers.More in detail, a first electrode 2 c, a piezoelectric/electrostrictivelayer 2 a, a second electrode 2 b, a piezoelectric/electrostrictivelayer 2 a, a first electrode 2 c, a piezoelectric/electrostrictive layer2 a, a second electrode 2 b are sequentially laminated, and apiezoelectric/electrostrictive operating portion comprising a pair ofelectrodes and a piezoelectric/electrostrictive layer is provided inthree layers in a direction in which composing films of the element arelaminated to be formed.

In the similar way with the device shown in FIG. 24, electrodes in thesame element and denoted by the same symbol are respectively appliedwith voltages of the same potential, and terminals causing an electriccurrent to flow to respective electrodes are all formed on a surface ofthe fixing plate 5 where elements are formed. Similarly with the deviceshown in FIG. 24, in the present embodiment as well, though a firstelectrode 2 c and a second electrode 2 b are respectively made to beshared and for common use by piezoelectric/electrostrictive operatingportions of the first layer, the second layer, and the third layer, theelectrodes may be respectively arranged independently. In this case,respective electrodes are called in sequence from the one closest to thethin plate portions 6 and 7, first, second, third, and fourth electrode.As to leading about of electrodes for a multi-layeredpiezoelectric/electrostrictive operating portions, as the devices shownin FIG. 24, and FIG. 25, electrodes that can be made for common use areto be made for common use so as to reduce the number of terminals, whichis a structure advantageous in driving and fabrication. On the otherhand, when all electrodes are independently provided, respectivepiezoelectric/electrostrictive operating portions can be operated byseparate signals, enabling more precise displacement control, which isan advantage. Of course, one end of a piezoelectric/electrostrictiveoperating portion exists on the fixing portion 5, the other end thereofis arranged on the thin plate portions 6 and 7, and the other end of thepiezoelectric/electrostrictive layer 2 a also exists on the thin plateportions 6 and 7, and are arranged to be within a range not exceedingthe entire length of the thin plate portions.

With increase of the number of layers, driving force can be increased,however, power consumption also increases therewith, and in actualimplementation, the number of the layers or the like may be suitablydetermined depending on application uses and specification of a device.Furthermore, in a device according to the present invention, as apparentfrom embodiments shown in drawings, even if the driving force isincreased by proving a multi-layered piezoelectric/electrostrictiveoperating portion, basically, a distance of the thin plate portions 6and 7 in width direction is unchanged, and therefore, the device isextremely preferable in positioning of a magnetic head for a hard diskand in applying for a control device for ringing suppression or thelike, for example, in a extremely narrow gap.

Moreover, a piezoelectric/electrostrictive element 2 comprising a firstelectrode 2 c and a second electrode 2 b respectively of comb-shapedstructure, as shown in FIG. 15, the first electrode 2 c and the secondelectrode 2 b being structured to be mutually opposed with apredetermined gap between teeth of each other can also used. Apiezoelectric/electrostrictive element according to the presentstructure is advantageous in reducing power consumption. Though thefirst electrode 2 c and the second electrode 2 b are arranged on theupper surface of the thin plate portions 6 and 7 and apiezoelectric/electrostrictive layer 2 a in FIG. 15, the electrodes maybe formed between the thin plate portions 6 and 7 and thepiezoelectric/electrostrictive layers 2 a, or the electrodes may bepreferably formed on the both surfaces one of which is upper surface ofthe piezoelectric/electrostrictive layers 2 a, and the another of whichis the surface between the thin plate portions 6 and 7 and thepiezoelectric/electrostrictive layers 2 a. In other words, in thepiezoelectric/electrostrictive element of the present structure,electrodes are formed at least on one major surface of at least apiezoelectric/electrostrictive layer 2 a. Further, apiezoelectric/electrostrictive element 2 shown in FIG. 16 also comprisesa first electrode 2 c and a second electrode 2 b respectively of acomb-shaped structure, and the first electrode 2 c and the secondelectrode 2 b are structured to be mutually opposed with a gap 13 ofpredetermined width between the teeth of each other. Whereas thepiezoelectric/electrostrictive element 2 is structured to have apiezoelectric/electrostrictive layer 2 a embedded in a gap 13 betweenthe first electrode 2 c and the second electrode 2 b, suchpiezoelectric/electrostrictive element 2 can also be preferably used.

As piezoelectric/electrostrictive elements 2 shown in FIG. 15 and FIG.16, when a piezoelectric/electrostrictive element 2 having comb-shapedelectrodes is used, a displacement of a piezoelectric/electrostrictiveelement 2 can be made larger by reducing a pitch D of the teeth of thecomb. When a voltage is applied across the comb-shaped electrodes, thevoltage is applied between the electrodes (for example, between thefirst electrode 2 c and the second electrode 2 b) causing an electricfield to operate on the piezoelectric/electro-strictive layer 2 a, basedon the electric field, a electric field induced distortion is induced onthe piezoelectric/electrostrictive layer 2 a, and thepiezoelectric/electrostrictive elements 2 described in FIG. 15 and FIG.16 have a function of, as a longitudinal effect of the electric fieldinduced distortion, mainly generating a distortion in a mode extendingin a direction of the electric field, namely in a direction parallel tothe main surfaces of the thin plate portions 6 and 7. Accordingly, if apiezoelectric/electrostrictive element of the structure is applied to adevice of the present invention, the distortion extending in a directiontoward the main surfaces of the thin plate portions 6 and 7 is convertedinto a bending displacement, which causes the thin plate portions 6 and7 to bend, and the driving portion 3 is made to be bent and displaced ina direction toward the outer space (toward the hole) having a joinedportion of the thin plate portions 6 and 7 with the movable portion 4 orof the thin plate portions 6 and 7 with the fixing portion 5 asfulcrums, and as the result, the movable portion 4 can be displaced in apredetermine direction. It should be noted that an element ordinarilyhaving a structure of comb-shaped electrodes is arranged such that thepitch direction of the comb-shaped teeth is in a direction in which thefixing portion is connected with the movable portion on the thin plateportions 6 and 7. By arranging in this manner, the extension distortionbased on the longitudinal effect of the electric field induceddistortion can be effectively utilized as a bending displacement.

Moreover, although a piezoelectric/electrostrictive element 2 is, asshown in the above-described drawings, preferably formed on the outersurface of a device 1, in a point that the driving portion 3 can bedriven in larger magnitude, the element may also be formed on the innersurface (namely inside the hole) of the device 1, or also on both theinner surface and the outer surface of the device 1. Further, when theelement is formed on the inner surface of the device 1, there is amethod, as to be described later, in that the element is simultaneouslyformed when the substrate portion, comprising at least the thin plateportions 6 and 7, the fixing portion 5, and the movable portion 4, isfabricated, so as to have the piezoelectric/electrostrictive operatingportion 2′ formed extending over the fixing portion 5 or the movableportion. As a material for a piezoelectric/electrostrictive layer, apiezoelectric material is preferably used, however, a electrostrictivematerial, a material of ferroelectric substance, or a material ofantiferroelectric crystal can also be used. However, when used for amagnetic head or the like, linearity between a displacement quantity ofthe movable portion and a driving voltage or an output voltage beingconsidered to be important, it is preferable to use a material of smalldistortion hysteresis, and a material having a coercive electric fieldof 10 kV/mm or less can be preferably used.

Specific piezoelectric/electrostrictive materials are lead zirconate,lead titanate, lead magnesium niobate, lead nickel niobate, lead zincniobate, lead manganese niobate, lead antimony stannate, lead manganesetungstate, lead cobalt niobate, barium titanate, sodium bismuthtitanate, potassium sodium niobate, strontium bismuth tantalate, and thelike, and they may be respectively used individually or contained in amaterial as mixture. Specifically, from a viewpoint of obtaining amaterial having high electromechanical coupling factor and piezoelectricconstant, and obtaining stabilized composition by virtue of smallreactivity with the thin plate portions (ceramics) when sintering apiezoelectric/electrostrictive layer, a material containing leadzirconate, lead titanate, and lead magnesium niobate as the majorcomponent, or a material containing sodium bismuth titanate as the majorcomponent is preferably used.

Moreover, any one of oxides and the like of the following may be usedindividually or as a material containing any ones of the oxides asmixture, namely, lanthanum, calcium, strontium, molybdenum, tungsten,barium, niobium, zinc, nickel, manganese, cerium, cadmium, chromium,cobalt, antimony, iron, yttrium, tantalum, lithium, bismuth, tin, andthe like. For example, by having lead zirconate, lead titanate, and leadmagnesium niobate, which are the major components, contained withlanthanum or strontium, adjustment of a coercive electric field,piezoelectric properties, or the like is made possible. It is of coursethat an attention is to be paid, when a material is to be selected, to arelationship between the Young's modulus Y2 of a material composing apiezoelectric/electrostrictive layer and the Young's modulus Y1 of amaterial composing the thin plate portions 6 and 7 so that the followingexpression is satisfied, namely;

1<Y1/Y2≦20.

Further, it is desirable that a material which is likely to be vitrifiessuch as silica or the like is refrained from adding. The reason is thata material such as silica or the like is liable to be reacted with apiezoelectric/electrostrictive material, when apiezoelectric/electrostrictive layer is thermally treated, thus thecomposition thereof is fluctuated, causing deterioration of thepiezoelectric properties.

On the other hand, an electrode of a piezoelectric/electrostrictiveelement is preferably composed of a metal which is solid at roomtemperature and superior in conductivity, such as, for example,aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc,niobium, molybdenum, ruthenium, palladium, rhodium, silver, tin,tantalum, tungsten, iridium, platinum, gold, lead, or the like, may beused singularly or as an alloy thereof, and further, a cermet materialcomposed of the above-described materials dispersed with the samematerial as for a piezoelectric/electrostrictive layer or the thin plateportions may also be used.

Selection of a material for an electrode in apiezoelectric/electrostrictive element is determined depending on amethod of forming a piezoelectric/electrostrictive element 2. Forexample, when a first electrode 2 c is first formed on the thin plateportions, and then a piezoelectric/electrostrictive layer 2 a is formedon the first electrode 2 c by sintering, it is necessary to use, as thefirst electrode 2 c, a metal of high-melting point such as platinum orthe like which is uninfluenced at the sintering temperature of thepiezoelectric/electrostrictive layer 2 a, however, a second electrode 2b, to be formed on the piezoelectric/electrostrictive layer 2 a afterthe piezoelectric/electrostrictive layer 2 a is formed, can be formed ata low temperature, thus a metal of low melting point, such as aluminum,gold, silver, or the like, can be used.

Further, as the thickness of an electrode may also cause not a smalldeterioration of a displacement of a piezoelectric/electrostrictiveelement, particularly for a second electrode 2 b shown in FIG. 14 to beformed after a piezoelectric/electrostrictive layer is sintered, orcomb-shaped electrodes 2 b and 2 c shown in FIG. 15, it is preferable touse a material of organic metal paste, for example, gold resinate paste,platinum resinate paste, silver resinate paste, or the like, whichassures a finer and thinner film after being sintered.

Although there are a variety of modes conceivable for electrode leadsfrom a piezoelectric/electrostrictive element 2, in a device 1 accordingto the present invention, where a piezoelectric/electrostrictive element2 is respectively formed on both of opposing thin plate portions 6 and7, one mode is that a first electrode 2 c is made for common use by twopiezoelectric/electrostrictive elements 2, and the electrode is drawnout to the fixing portion 5 side of one surface where the hole 8 isapertured, and a second electrode 2 b is directly drawn out to thefixing portion 5 side of a surface where respectivepiezoelectric/electrostrictive elements 2 are formed (FIG. 9). Anotherembodiment (FIG. 13) is that both the first electrode 2 c and the secondelectrode 2 b are drawn out to one surface of the fixing portion 5 sidewhere the hole 8 is apertured. In such embodiments, a portion of thefixing portion 5 side of the other surface where the hole 8 is apertured(symbol 9 in FIG. 13) is unformed of any electrode, and the portion isavailable for a device to be fixed, and therefore the device can bereliably fixed. Moreover, if the device is fixed on one surface sidewhere the hole 8 is apertured, bonding of electrodes and the fixing canbe simultaneously performed, which is advantageous in compaction and thelike.

Further, there may also be a mode, as shown in FIG. 17(a), where both asecond electrode 2 b and a first electrode 2 c are drawn out so as to bejuxtaposed on the fixing portion 5 side of surfaces where respectivepiezoelectric/electrostrictive elements 2 are formed, or a mode, asshown in FIG. 17(b), where a second electrode 2 b and a first electrode2 c are respectively drawn out separately to the movable portion 4 sideand the fixing portion 5 side of respective surfaces wherepiezoelectric/electrostrictive elements are formed.

3. Method of Fabricating the Device

Now, a method of fabricating a device of the present invention isdescribed.

It is preferable that the device of the present invention comprisesrespective members composed of a ceramic material, and as theconstituting elements of the device, substrate members except for apiezoelectric/electrostrictive element, namely thin plate portions, afixing portion, and a movable portion are fabricated by use of theceramic green sheet laminating method, and more preferably fabricated bylaminating integration by simultaneous sintering. On the other hand, itis preferable that a piezoelectric/electrostrictive element andrespective terminals are fabricated by use of film forming methods for athin film, a thick film, or the like for forming such members intofilm-like members. The ceramic green sheet laminating method is capableof integrally forming the above-described respective substrate membersof a device, and is an easy method in securing high reliability ofjoined portions and stiffness of the device, as there is scarcely anystate variation with time at joined portions of respective members. In adevice according to the present application, joined portions of the thinplate portions, which constitute the driving portion, with the fixingportion and the movable portion function as the fulcrums for developinga displacement. So, bonding reliability at the joined portions is a veryimportant point dominating characteristics of the device. Further, asthe method is superior in productivity and moldability, a device of apredetermined shape can be fabricated thereby in shorter time and betterreproducibility. It should be noted that although terminology of “a thinplate” and “a thin plate portion” are used in the specification of thepresent application, the former is used, in principle, for a memberrelated to a green sheet in the method of fabrication, while the latterindicates a portion constituting the driving portion together with apiezoelectric/electrostrictive element in a laminated body.

(1) Method of Fabricating the Laminated Body

To start with, in order that the Young's modulus Y1 of a materialcomposing the thin plate portions and the Young's modulus Y2 of amaterial composing the piezoelectric/electrostrictive layer satisfiesthe following expression, namely;

1<Y1/Y2≦20,

a slurry is prepared by adding and mixing a binder, a solvent, adispersant, a plasticizer, or the like into ceramic power of selectedzirconia or the like, the slurry is then processed for degassing, andused for fabricating a ceramic green sheet having a predeterminedthickness, by way of the reverse roll coater method, the doctor blademethod, or the like.

Then, the ceramic green sheet is machined into a variety of shapes, forexample, shapes as shown in FIG. 18, by means of stamping using a die(punching), laser machining, or the like. It should be noted that thefabrication of a laminated body may basically be relied on a methoddisclosed in the specification of Japanese Patent Application No.11-375581 filed on Dec. 28, 1999. For reference, the contents of theapplication are hereinafter quoted.

In FIG. 18(a), a ceramic green sheet 101 exemplarily shows a ceramicgreen sheet mainly to be a thin plate after being sintered, and aceramic green sheet 102 having at least one rectangular hole 103 formedthereon exemplarily shows one ceramic green sheet for members to be amovable portion and a fixing portion. With the ceramic green sheet 102,a plurality of devices can be obtained at one time, or at least onedevice having a plurality of movable portions can be obtained, byforming one row or more holes 103 so as to be juxtaposed. By use of atleast two ceramic green sheets to be thin plates, and at least oneceramic green sheet having at least one hole formed thereon, prepared inadvance, and by laminating at least one ceramic green sheet having atleast one hole formed thereon, for example, between at least two ceramicgreen sheets to be the thin plates, a ceramic green laminated bodycomprising ceramic green sheets to be a pair of thin plates and a seriesof ceramic green sheets having at least one hole formed thereon may beprepared.

Of course, there is no specific limitation whatsoever on method ofpreparing the ceramic green laminated body, in other words, onlaminating sequence of the ceramic green sheets to be the thin platesand the ceramic green sheets having at least one hole formed thereon,and ordinarily, lamination is possible at an optional sequence so longas the processes to follow are not influenced by the laminated body.

For example, steps preparing the ceramic green laminated body include, astep for laminating ceramic green sheets to be a pair of thin plates,mutually opposed, a step for laminating ceramic green sheets to be apair of thin plates on the outermost layers, mutually opposed, a stepfor preparing a ceramic green sheet to be a thin plate laminated with atleast one ceramic green sheet having at least one hole formed thereon, astep for preparing a ceramic green sheet to be a thin plate laminatedwith the desired number of ceramic green sheets having at least one holeformed thereon, a step for preparing at least one ceramic green sheethaving at least one hole formed thereon laminated by ceramic greensheets to be a pair of thin plates on the outermost layer thereofmutually opposed, a step wherein two laminated bodies A prepared by aceramic green sheet to be a thin plate laminated with at least oneceramic green sheet having at least one hole formed thereon areprepared, and one sheet of a ceramic green sheet having at least onehole formed thereon or a laminated body B laminated with a plurality ofsaid ceramic green sheets is prepared, and when the two laminated bodiesA are laminated so as to have respective thin plates respectivelyforming the outermost layers, the one sheet of a ceramic green sheethaving at least one hole formed thereon or the laminated body B isintervened, and the like.

Furthermore, when a device according to the present invention isfabricated by such ceramic green sheet laminating method, when forming ahole by laminating thick sheets, difference in dimensions betweenlengths of a pair of thin plate portions governing the driving portionis likely to be caused, by chance, by shrinkage of ceramic green sheets,by deterioration in machining precision derived from difference indimension precision accompanied to machining of thick ceramic greensheet, or by shifting of positions due to deformation of sheets whilelaminating, or the like. The difference in dimensions of the pair ofthin plates is displayed per se as the difference of the displacement inthe right-to-left direction (X-axis direction), and further makes themovable portion liable to contain a component toward the rotationaldirection in the displacement mode thereof, thus the movable portion ismade difficult to dominantly displace toward a specific axis.

These problems are countered by employing a step wherein, whenlaminating at least a plurality of ceramic green sheets having at leastone hole formed thereon, a ceramic green sheet mounted on a plastic filmand having at least one hole formed thereon is laminated on a surface tobe the outermost surface of the ceramic green laminated body having atleast one hole formed thereon such that the plastic film is made to be anew outermost layer, and after the hole is accurately positioned, theplastic film is removed, or a step wherein a ceramic green sheet mountedon a plastic film and having at least one hole formed thereon islaminated on a ceramic green sheet to be the thin plate such that theplastic film is made to be an outer layer, and after the hole isaccurately positioned, the plastic film is removed, thus not onlydeformation of a ceramic green sheet at handling thereof can besubstantially avoided, but also both surfaces to be the outermostsurfaces respectively can be made to be in the same shape, enablingaccurate positioning of the hole, thus lamination precision is improved,and dimensions are stabilized by improvement of the machining precision,with a result that characteristics of the device, for example,displacement characteristics, are improved.

Further, of the above-described methods of fabrication using the plasticfilm, the former is higher in laminating efficiency required by the timethe final laminated body is obtained, and effective in reducing thenumber of steps. On the other hand, the latter is advantageous inproviding a bonding auxiliary layer, to be described hereinafter, inorder that the bonding property at a laminating interface is ensured.

In other words, as to the number of laminating steps, the former is moreefficient, since a ceramic green sheet formed on a plastic film can belaminated with the other ceramic green sheet having a hole at one time,and lamination with opposing surfaces where plastic films are removedafter lamination, and with ceramic green sheets to be thin plates can berespectively performed also at one time, thus all lamination requiredcan be done by minimum two times lamination. However, the number oflaminations for the latter is minimum three times, one more than theformer, as mutually opposing thin plates require separate laminationsfor the ceramic green sheet to be a thin plate and for the ceramic greensheet mounted on a plastic film and having a hole, respectively, andthereafter the ceramic green sheet having a hole formed thereon islaminated.

Moreover, as to the adhering auxiliary layer for improving thelaminating property of ceramic green sheets, ordinarily, the adheringauxiliary layer is formed substantially on entire surface of a ceramicgreen sheet prior to machining of the hole or the like, and thereafter ahole of a predetermine shape is formed by punching or the like using adie, and then a predetermined number thereof are laminated, however,when this is applied to the former method, after the film is exfoliatedand removed, a bonding auxiliary layer is required to be formed on alaminating surface with a thin plate. At this time, despite that a shapeis accurately produced by die machining or the like, with the bondingauxiliary layer formed, the possibility is larger that the shapeprecision is lowered. Although there is means to provide a bondingauxiliary layer for the green sheet to be the thin plate, ordinarily thethickness variation of the bonding auxiliary layer being larger than thethickness variation of the green sheet to be the thin plate, not onlytotaled thickness variation is increased, but also the thin plate isthickened as much as the thickness of the bonding auxiliary layer, thusthe characteristics of the device are lowered. Contrarily, when this isapplied to the latter, a bonding auxiliary layer can be formed on theceramic green sheet, in a state the ceramic green sheet is mounted on aplastic film, thus a hole can be machined after the bonding auxiliarylayer is formed. Accordingly, the precision of the hole is secured bythe precision of a die, and the green sheet to be the thin plate isuntouched whatsoever, enabling compatibility of high laminatingreliability and high dimension precision. As to the surface where aplastic film is exfoliated and removed, laminating reliability issecured by a bonding auxiliary layer formed on a separate ceramic greensheet having a hole formed thereon to be laminated on the surface.

Though both the former method and the latter method have a common targetof obtaining stabilized shape of the thin plate portions, there arerespective features in steps of fabrication, and the methods can besuitably selected depending on structure and the like of a laminatedbody.

It should be noted that a ceramic green sheet mounted on a plastic filmand having at least one hole formed thereon includes not only a ceramicgreen sheet having a hole formed thereon, prepared from a ceramic greensheet on a plastic film by die-punching machining or laser machining,but also a ceramic green sheet having at least one hole, formed inadvance in a predetermined shape, with a plastic film applied thereon.Further, the plastic film is preferably a poly(ethylene-terephthalate)film from the points of exfoliating property, mechanical strength, orthe like. Furthermore, the ceramic green sheet mounting surface of theplastic film is preferably a film coated by a mold-releasing agentcontaining silicone or the like a s a component for improvingexfoliating property of the green sheet. Further, the thickness of theceramic green sheet on the plastic film is preferably thinner, anddesirably, the thickness is more preferably equivalent to the thicknessof the green sheet for the thin plate. The reason is that by thinningthe ceramic green sheet, machining precision of the ceramic green sheetper se can be improved. Furthermore, in order to facilitate handling ofrespective green sheets, specifically the ceramic green sheets to be thethin plates, to prevent elongation and sagging of a sheet, and tostabilize the shape of the thin plate portions, it is preferable tohandle the sheets attached to the above-described plastic film.

Specific examples when a ceramic green laminated is prepared arehereinafter described. Examples quoted herein are merely illustrations,and it goes without saying that a case when a ceramic green sheet isprepared is not limited in any way to these examples.

LAMINATION EXAMPLE 1

After sequentially laminating a ceramic green sheet (hereinafterreferred to as “GS”) for the thin plates 1, GS1 having a hole formedthereon, GS2 having a hole formed thereon, GS3 having a hole formedthereon, GS4 having a hole formed thereon, and GS2 for the thin plates,as shown in FIG. 19, a ceramic green laminated integrated body isobtained by compressing.

LAMINATION EXAMPLE 2

Step 1: After GS1 for thin plates is laminated with GS1 having a holeformed thereon, a ceramic green laminated body is obtained bycompressing.

Step 2: After GS4 having a hole formed thereon is laminated with aceramic green sheet 2 for the thin plates, a ceramic green laminatedintegrated body is obtained by compressing.

Step 3: A ceramic green laminated integrated body obtained in Step 1,GS2 having a hole formed thereon, GS3 having a hole formed thereon, anda ceramic green laminated integrated body obtained in Step 2 aresequentially laminated, and a ceramic green laminated integrated body isobtained by compressing.

LAMINATION EXAMPLE 3

Step 1: GS1 having a hole formed thereon, GS2 having a hole formedthereon, GS3 having a hole formed thereon, and GS4 having a hole formedthereon are sequentially laminated, and a ceramic green laminatedintegrated body is obtained by compressing.

Step 2: GS1 for the thin plates, a ceramic green laminated integratedbody obtained in step 1, and GS2 for the thin plates are sequentiallylaminated, and a ceramic green laminated integrated body is obtained bycompressing.

LAMINATION EXAMPLE 4

Step 1: GS2 having a hole formed thereon is laminated with GS3 having ahole formed thereon, and a ceramic green laminated integrated body isobtained by compressing.

Step 2: GS1 for the thin plates, GS1 having a hole formed thereon, aceramic green laminated integrated body obtained in step 1, GS4 having ahole formed thereon, and GS2 for the thin plates are sequentiallylaminated, and a ceramic green laminated integrated body is obtained bycompressing.

The ceramic green laminated integrated bodies obtained in theabove-described examples 1 to 4 are sintered and integrated sinteredbodies are obtained. However, the above-described examples do not showall methods of fabricating the devices according to the presentinvention, and there is no specific limitation whatsoever on the numberand the

The number and the sequence of the compressing are suitably determinedso that desired structure can be obtained, depending on structure, forexample, the shape of the hole, the number of sheets of the ceramicgreen sheet having a hole formed thereon, the number of sheets of theceramic green sheet for the thin plates, or the like.

Of course, the shape of the hole is not required to be the same for all,and is determined depending on desired functions. Moreover, there is nospecific limitation whatsoever on the number of sheet and the thicknessof respective ceramic green sheets.

As the above-described compressing can be further improved of thelaminating properties thereof by heating, compressing under heating canbe also advantageously employed. Furthermore, it is also preferable touse a bonding auxiliary layer, as the laminating properties of a ceramicgreen sheet interface can be improved by coating, or printing, a paste,a slurry or the like containing ceramic powder, preferably, of the sameor similar composition as the one used for the ceramic green sheet, inview of securing reliability, and a binder as the major component, on aceramic green sheet to form a bonding auxiliary layer thereon.

Further, a protrusion may be provided at a portion on the outer surfaceof the layer of at least on one side of the outermost layer of theceramic green laminated body, excepting at least the thin plates. Adevice according to the present application has apiezoelectric/electrostrictive element formed on the outer surface ofmutually opposing thin plate portions, ordinarily by known means such asthe screen printing method, or the like, so, when thepiezoelectric/electrostrictive element is formed, for example, by thescreen printing method, a damage to elements can be prevented, as thesurface, where the elements are formed, formed on the opposite surface,is prevented from touching directly a bed such as a stage for printing,a setter for sintering, or the like, by the protrusion formed.Furthermore, by suitably selecting the height of the protrusion, thethickness of the elements can be controlled. Although the protrusion canbe formed on a sintered green laminated body, namely on a ceramiclaminated body, it is more preferable to have the protrusion formed on agreen laminated body to be sintered and integrated from the points ofstability of the structure and stability in dimensions.

An example of a method of fabricating a device according to the presentinvention is briefly described with reference to FIGS. 20(a) to 20(d),and FIG. 21. FIG. 20(a) shows an exemplary perspective view of astructure of a ceramic green laminated body 108 prior to sintering, FIG.20(b), and FIG. 20(c) show perspective views of a structure of alaminated sintered body 132 with piezoelectric/electrostrictive elementsformed thereon, FIG. 20(d) shows an exemplary perspective view of astructure of a ceramic green sheet having a hole formed thereon.

As shown in FIG. 20(a), a ceramic green sheet 101 to be a thin plateafter being sintered, a ceramic green sheet 102, maybe comprising aplurality of sheets, having at least one hole formed thereon, and aceramic green sheet 101 to be a thin plate after being sintered, arelaminated in the sequence while positioning utilizing reference holes104, and integrated by use of previously described method such asthermo-compression bonding or the like, thus a ceramic green laminatedbody 108 can be obtained. When the ceramic green laminated body 108 istoo thick, a ceramic green laminated body 105 is halved, in advance, toform an upper and a lower ceramic green laminated bodies, as shown inFIG. 21, and the halved bodies are joined so as to have the holes facedeach other, and a final ceramic green laminated body 108 may beobtained.

As for the ceramic green laminated body 108, it is necessary thatcommunicating holes 106 for communicating portions of ceramic greensheet 102 to be holes 103 with the outer space are formed in advance onthe ceramic green sheet 102 by punching by use of a die or the like, orthe communicating holes 106 are bored after a plurality of the ceramicgreen sheets 102 are laminated. However, as long as respective holes 103are communicated with the outer space, there is no specific limitationwhatsoever about shape of the communicating holes 106, and in additionto a type in which respective communicating holes run through aplurality of the holes as shown in FIG. 20(a), there may be other typessuch as shown in FIG. 20(d) where the holes 103 are respectivelycommunicated with the outer space. A ceramic green laminated body 108thus integrated by these methods is sintered at a temperature around1200 to 1600° C. as to be described hereinafter. However, there may bean occasion when a ceramic laminated body 109 thus obtained after beingsintered has an unintended warping. In the case, it is preferable thatthe ceramic laminated body 109 is flattened by being re-sintered(hereinafter referred to as “warping correction”) with a weight placedthereon at a temperature close to the above-described sinteringtemperature. In this warping correction, it is preferable to use aporous ceramic plate such as a planar alumina or the like. Further, inwarping correction, in addition to performing the warping correctionfollowing the sintering, it is also preferable to flatten simultaneouslywith sintering, with the above-described weight placed thereon inadvance.

(2) Formation of Piezoelectric/Electrostrictive Element

As to a piezoelectric/electrostrictive element, when a device of thepresent invention is fabricated, a piezoelectric/electrostrictiveelement 107 can be formed in a desired number on the surface of thinplates of a ceramic laminated body 109 by use of a thick film method,such as the screen printing method, the dipping method, the coatingmethod, the electrophoresis method, or the like, or a thin film method,such as the ion-beam method, the sputtering method, the vacuumdeposition method, the ion-plating method, the chemical vapor depositionmethod (CVD), plating, or the like (refer to FIG. 20(b)). However, FIG.20(b) only exemplarily shows a piezoelectric/electrostrictive element107, and does not show accurate arrangement of thepiezoelectric/electrostrictive element 107. In addition, although a thinplate 131 of a ceramic laminated body 109 is denoted by solid lines inFIG. 20(b) and FIG. 20(c), this is only to understandably describe theportion, and as the member is integrally sintered, there is no suchboundary, which is a matter of course. Further, it is required that atleast one end of a piezoelectric operating portion of thepiezoelectric/electrostrictive element 107 exists on the fixing portionor the movable portion, the other end thereof is arranged on the thinplate portions 6 and 7, and an end of a piezoelectric/electrostrictivelayer of the other end side thereof is formed by the above-describedmethod so as also to be on the thin plate portions within a range notexceeding the entire length of the thin plate portions 6 and 7. Ofcourse, in the case, it is necessary to select materials such that theYoung's modulus Y2 of a material composing thepiezoelectric/electrostrictive layer and the Young's modulus Y1 of amaterial composing the thin plate portions satisfy the followingexpression, namely;

1<Y1/Y2≦20.

By forming a piezoelectric/electrostrictive element in this manner, thepiezoelectric/electrostrictive element and the thin plate portions canbe integrally joined and arranged without using an organic adhesive suchas an epoxy resin, an acrylic resin, or the like, thus reliability andreproducibility are secured, and integration is facilitated, which areadvantageous. Specifically, in a method of fabrication in the presentinvention, it is preferable that at least apiezoelectric/electrostrictive layer 2 a of thepiezoelectric/electrostrictive element 107 is formed by the previouslydescribed thick film method, and a ceramic laminated body and apiezoelectric/electrostrictive element are integrated by heat treatmentwithout use of an organic adhesive. It is more preferable that apiezoelectric/electrostrictive layer in which glass is not contained canbe composed by integration by heat treatment at least without addingglass frit to the piezoelectric/electrostrictive layer, thusdisplacement characteristics can be advantageously improved. The reasonis that according to these thick film methods, apiezoelectric/electrostrictive layer can be formed using a paste, aslurry, a suspension, an emulsion, a sol, or the like, containingparticles or powder of piezoelectric ceramics of average particle sizeof 0.01 to 5 mm, preferably 0.05 to 3 mm as the major component, thusfavorable piezoelectric operating characteristics can be obtained.Specifically, the electrophoresis method has an advantage that a filmcan be formed in high density and in high shape precision. On the otherhand, the screen printing method is employed as the most preferablemethod of fabricating a device according to the present invention, as itenables simultaneous formation of a film and a pattern, and also enablesformation of a plurality of piezoelectric/electrostrictive elements onthe same ceramic laminated body with ease.

Specifically, a piezoelectric/electrostrictive element can be formed ina method where a ceramic green laminated body 108 is sintered at apredetermined conditions, preferably at a temperature of 1200 to 1600°C., then in sequence, a first electrode is printed and sintered at apredetermined position on the surface of a thin plate 131, then apiezoelectric/electrostrictive layer is printed and sintered, further asecond electrode is printed and sintered, thus apiezoelectric/electrostrictive element can be formed. Further, anelectrode lead for connecting an electrode with a driving circuit isprinted and sintered. Here, if a material for respective members isselected so as to have gradually lowering sintering temperatures, suchas platinum (Pt) for a first electrode, lead zirconate titanate (PZT)for a piezoelectric/electrostrictive layer, gold (Au) for a secondelectrode, and further silver (Ag) for an electrode lead, re-sinteringof a material once sintered previously will not occur at any sinteringstage, and thus generation of troubles such as exfoliation oraggregation of an electrode material or the like can be prevented.

It should be noted that, by selecting a material, it is possible tosequentially print respective members and electrode leads of a precursor(formed body to be sintered) to be integrally sintered at a time, whilerespective electrodes and the like may be provided at a lowertemperature after a piezoelectric/electrostrictive layer is formed.Further, respective members and electrode leads of thepiezoelectric/electrostrictive element may be formed by the thin filmmethod, such as the sputtering method, the deposition method, or thelike, and in this case, heat treatment is not necessarily required.Moreover, it is also preferable that a precursor of thepiezoelectric/electrostrictive element 107 is formed in advance at aposition finally to be the thin plate portions of the ceramic greenlaminated body 108, so that the ceramic green laminated body 108 and thepiezoelectric/electrostrictive element are simultaneously sintered.

The simultaneous sintering may also be performed together with allcomposing films of the precursor of the piezoelectric/electrostrictiveelement 107, and furthermore, available methods include a method whereonly a first electrode and a ceramic green laminated body 108 aresimultaneously sintered, a method where composing films, excepting asecond electrode, and a ceramic green laminated body are simultaneouslysintered, and the like. Methods to have a precursor of apiezoelectric/electrostrictive element 107 and a ceramic green laminatedbody 108 simultaneously sintered include a method where apiezoelectric/electrostrictive layer is formed by the tape moldingmethod by use of a slurry material, the pre-sinteringpiezoelectric/electrostrictive layer is laminated on a predeterminedportion of the ceramic green sheet 101 to be the thin plate bythermo-compression bonding or the like, then the ceramic green sheet 102having the hole 103 formed thereon is laminated and compressed thereon,and then the laminated body is simultaneously sintered, thus a movableportion, a driving portion, thin plate portions, and apiezoelectric/electrostrictive layer are simultaneously fabricated.However, in this method, electrodes are to be formed in advance on thethin plate and/or a piezoelectric/electrostrictive layer. Further, inaddition to the above-described method, one of the other methods is thatelectrodes and a piezoelectric/electrostrictive layer which arerespectively composing layers of a piezoelectric/electrostrictiveelement are formed by screen printing method on a position, at leastfinally (after being sintered) to be the thin plate portions, of aceramic green laminated body 108, then the entirety is simultaneouslysintered. However, a method where a piezoelectric/electrostrictiveelement is formed on an already sintered ceramic laminated body 109 by afilm forming method, preferably by the screen printing method, ispreferably employed, as higher pattern precision and uniform filmthickness can be obtained thereby and distortion as a structure can bereduced.

Though sintering temperature of respective films composing apiezoelectric/electrostrictive element is suitably determined dependingon a material composing the element, generally it is 600 to 1400° C.,and for a piezoelectric/electrostrictive layer, preferably 1000 to 1400°C. In this case, in order to control the composition of apiezoelectric/electrostrictive layer, it is preferable that sintering isperformed under existence of an evaporation source of a material of thepiezoelectric/electrostrictive layer. It should be noted that when apiezoelectric/electrostrictive layer and a ceramic green laminated body108 are simultaneously sintered, sintering conditions of the both are tobe matched.

When fabricating a device having a piezoelectric/electrostrictiveelement formed respectively on both thin plate portions of a pair ofmutually opposing thin plate portions, a precursor of apiezoelectric/electrostrictive layer, precursors of electrode films, andthe like may be advantageously printed on both sides of a ceramiclaminated body 109, however, in such case, it is preferable that acounter measure is taken lest the precursor of thepiezoelectric/electrostrictive layer, the precursors of electrodes, andthe like should stick or contact a printing stage, by printing in eitherof the methods of {circle around (1)} that printing is performed on aprinting stage where a cavity is provided thereon, or {circle around(2)} that a frame-shaped convex is formed on a periphery of a printingposition on at least one of printing surface of a ceramic laminatedbody, and a surface where the convex is formed is first printed followedby printing of the other surface, or the like. Moreover, specifically insintering the above-described piezoelectric/electrostrictive layer, whenpiezoelectric/electrostrictive elements are formed on both sides of aceramic laminated body, it is preferable that sintering atmosphere ofthe both sides is made to be the same, lest there should be differencein the piezoelectric characteristics of respectivepiezoelectric/electrostrictive elements on the both sides. For example,ordinarily, a ceramic laminated body with a precursor of apiezoelectric/electrostrictive element (film) formed thereon is placedon a board such as a setter or the like for being sintered, in thiscase, gaps between setters to be interstacked are to be adjusted by aspacer or the like so that a space between apiezoelectric/electrostrictive layer and the setter is made to be same.

Although the above-described are specific examples of film formingmethods preferably employed for the present invention, fabrication ofthe device is also possible by a method wherepiezoelectric/electrostrictive elements sintered in advance as separatebodies are adhered to predetermined positions of a ceramic laminatedbody 109 by an adhesive such as an organic resin or the like.

(3) Cutting the Laminated Body

A previously described laminated sintered body 132 having apiezoelectric/electrostrictive elements is, after thepiezoelectric/electrostrictive element and electrode leads are subjectedto treatments of coating, shielding, and the like, cut in a laminatingdirection of a ceramic green sheet, so as to have a rectangular hole 133apertured on a side of the laminated body, thus a plurality of thedevices can be simultaneously obtained (FIG. 20(c)). As for methods ofcutting, in addition to the dicing machining, the wire-saw machining(mechanical machining), or the like, the machining by the YAG laser, theexcimer laser, or the like, or the electron-beam machining can beemployed. When cutting into respective desired units, it is preferablethat the cut bodies are thermally treated at a temperature of 300 to800° C. after being cut. The reason is that the machining is likely tocause a defect such as a micro-crack or the like inside the sinteredbody, and the defect can be removed by the heat treatment, thusimproving reliability thereof. Further, after the heat treatment, it ispreferable to leave the cut bodies for at least about 10 hours at atemperature around 80° C. for aging treatment. By this treatment, avariety of stress or the like suffered during the processes offabrication may be relieved, thus contributing to improvement of thecharacteristics.

When fabricating a device of the present invention, cutting is performedso as to have a hole of a desired shape, for example, arectangular-shaped hole 133, apertured on a side of a laminated body.Such cutting has advantages of not only separating a plurality ofdevices but also simultaneously forming thin plate portions and the holeof the device, for example, in case of the device shown in FIG. 8, thethin plate portions 6 and 7 and a hole 8. This method is also preferablesince a structure which is otherwise complicated because it has two ormore rectangular solids combined by thin plates, and therefore isdifficult to be fabricated, is simply obtained.

Moreover, by suitably changing the number of formations and the positionof formation of a hole 103 in a ceramic green sheet 102, or the cuttingposition of a laminated sintered body 132 having apiezoelectric/electrostrictive element 107, a device having a pluralityof driving portions or a device having different lengths of the drivingportion can be formed with extreme ease. Further, by simultaneouslycutting a ceramic laminated body 109 and apiezoelectric/electrostrictive element 107, a device having the thinplate portions and the piezoelectric/electrostrictive element in thesame width can be fabricated with ease, which is preferable. Suchcutting may also be applied to a green state prior to the sintering,however, it is preferable to apply it to a sintered body, in order toimprove dimension precision and to prevent release of particles ofrespective ceramic powder.

Furthermore, a device of the present invention can also be fabricatednot only by using a ceramic green sheet as described above, but also byusing the pressure molding method or the cast molding method by use of ashaping die, the injection molding, photolithography, or the like.Further, although the device can also be fabricated by another method ofbonding respective members prepared as separate bodies, the method isproblematical also in reliability as a fracture or the like is likely tooccur at a joined portion, in addition to low productivity.

4. Application Example of the Device

Lastly, as an application example of a device of the present invention,an example in which a device of the present invention is applied to adisplacement element for an optical shutter is described with referenceto the drawings. Meanwhile, it could be easily understood that FIGS.22(a) and 22(b), and FIGS. 23(a) to 23(c) exemplarily show devices ofthe present invention applied to displacement elements for opticalshutters, and do not accurately show structures according to the presentapplication. By the way, “optical shutter” in the present specificationmeans a functional element for controlling transmitting and shielding oflight by the relative movement of two shields, and can function as anoptical switch or an optical diaphragm, as the optical shutter canperform ON/OFF control or control of quantity of the light.

When a device of the present invention is mounted on an optical shutter,at least one out of two shields is fixed on a movable portion of adevice of the present invention.

For example, an optical shutter 110 shown in FIGS. 22 (a) and (b),comprises two units 111A and 111B respectively provided with a device ofthe present invention and a shield, and two shields 113A and 113B arerespectively mounted on movable portions 114A and 114B of the device,and arranged to have respective planar surfaces to be parallel, andparts of the planar surfaces to be mutually overlapped against theincident direction of the light L.

Although the optical shutter 110 shields the light L in the state shown,by applying a voltage of the same phase topiezoelectric/electrostrictive elements 112A and 112B formed on drivingportions of the devices, the shield 113A moves to the left in FIG.22(a), and the shield 113B moves to the right in FIG. 22(a), causing theoverlapping condition of the shields 113A and 113B to change, thusenabling ON/OFF control and control of quantity of the light.

Further, an optical shutter 120 shown in FIG. 23(a) comprises two units121A and 121B respectively provided with a device of the presentinvention and a shield, and two shields 123A and 123B are respectivelymounted on movable portions 124A and 124B, and arranged to have mutualplanar surfaces to be parallel, and to have the entirety of the planarsurfaces to be totally overlapped against the incident direction of thelight L. And slits 125A and 125B are respectively formed at opposingpositions on the shields 123A and 123B.

Although the optical shutter 120 transmits the light L through the slits125A and 125B in the state shown in FIGS. 23(a) and (b), by applying avoltage of the same phase to piezoelectric/electrostrictive elements122A and 122B formed on the driving portions of the device, the shield123A moves to the left and shield 123B moves to the right in FIG. 23(b),causing the overlapping condition of the slits 125A and 125B to change,thus enabling ON/OFF control and control of quantity of the light. FIG.23(c) shows a state where a part of the light is transmitted, and bychanging shapes and formation positions of the slits 123A and 123B, thelight L can be completely shielded.

Contrarily, in the state shown in FIGS. 23(a) and (b), the slits 125Aand 125B may be constituted not to overlap each other but to shield thelight L, and may be structured such that the slits 125A and 125B areoverlapped by the movement of the shields 123A and 123B enabling thelight L to transmit. In examples related to FIGS. 22(a) and (b), andFIGS. 23(a), (b), and (c), examples where two shields are fixed onrespective devices are shown, however, in an optical shutter of thepresent invention, at least one shield is fixed on a device, and only bymoving the one shield, transmitting and shielding of the light can becontrolled. However, it is more preferable to have both shields fixed onthe devices, as the relative movement quantity of the shields can beincreased. Though the optical shutter comprises two units in theexamples of FIGS. 22(a) and (b), and FIGS. 23(a), (b), and (c), theshutter may comprise three or more units. In this case, by setting avariety of moving directions for a plurality of shields, the opticalshutter may also be used as an optical diaphragm or the like havingvaried degrees of aperture of the overlapped portion. An optical shutterof the present invention can suppress operation of a shield in aflapping direction, as the shield is provided on a movable portion of adevice of the present invention. In other words, as the shield alwaysmoves facing straight to the incident direction of the light, ON/OFFcontrol and control of quantity of the light are made possible in higherprecision, thus the optical shutter can be preferably used.

As a device according to the present invention has a feature of having ahigh stiffness in the width direction of a thin plate, namely in theY-axis direction, the device has a structure that enables strongerbonding when functional members such as a sensor, a magnetic head, orthe like are fixed to the device, or when the device per se is mountedon another structure. In addition, because of this stiffness, the devicealso has a feature that a member of relatively large mass can also bemounted. Further, as the stiffness in the thickness direction is, incomparison with the width direction, relatively small, an effect isdisplayed that, when the device is driven based on the directionalproperty of the stiffness, the displacement component in the Y-axisdirection, namely a flapping component, is effectively suppressed.

Moreover, a device according to the present invention has one end of apiezoelectric/electrostrictive operating portion arranged on the fixingportion or the movable portion, and the other end of thepiezoelectric/electrostrictive operating portion arranged on the thinplate portion, a displacement of a piezoelectric/electrostrictiveelement is developed having the joined portion of the fixing portionwith the thin plate portion, or the joined portion of the movableportion with the thin plate portion as the fulcrum. As the displacementmechanism has a structure that makes the thin plate portion bend anddisplaces such that the joined portion of the movable portion with thethin plate portion is largely displaced in a direction toward the outerspace, the movable portion can be made to be displaced in still largermagnitude.

In addition, as a device of the present invention has a displacementpath of the movable portion made substantially parallel to the fixingportion, the device has a feature that operation with very littlepitching can be realized when a member such as a sensor, and the like isfixed at the tip of the movable portion. The displacement mechanismwhich enables a displacement substantially in parallel is derived fromthe above-described arrangements of a piezoelectric/electrostrictiveoperating portion and a piezoelectric/electrostrictive layer, and therelationship of the Young's moduli of a material of the thin plateportion and a piezoelectric/electrostrictive material, and is madepreferably attainable by making the displacement mode of the thin plateportion due to operation of a piezoelectric/electrostrictive elementhave the inflection point for the displacement. The structure, whichenables operation in substantially parallel, effectively displaces alimited portion of low stiffness of the thin plate portion under theabove-described conditions, and therefore, displacement efficiency isextremely high, and as the result, an effect is displayed that themovable portion is displaced in still larger magnitude. Moreover, as thesubstrate comprising a movable portion, thin plate portions, and afixing portion is an integrated body by simultaneous sintering, and apiezoelectric/electrostrictive element is also integrated with the thinplate portion by heat treatment without using any adhesives, thusrespective members are unrelated with adhering integration, andtherefore the device has features that joined portions are superior inreliability, and have high stiffness, and as the result, high resonantfrequency as a structure is facilitated. In other words, the device isof a structure where a large displacement in a specific one axis can beobtained with a relatively low voltage, and which is superior inresponsibility, and has a small variation in characteristics forelongated usage.

Therefore, the device can be utilized not only for active elements suchas a variety of transducers, a variety of actuators, frequency regionalfunctional members (filters), transformers, vibrators and resonators forcommunication and power uses, oscillators, discriminators, and the like,but also as sensor elements for a variety of sensors, such asultra-sonic sensors and acceleration sensors, angular velocity sensorsand impact sensors, mass sensors, and the like, and can be preferablyutilized for a variety of actuators used specifically for mechanisms fordisplacement adjustment or angular adjustment, or positioning adjustmentof a variety of precision parts of optical apparatuses, precisionapparatuses, and the like.

What is claimed is:
 1. A piezoelectric/electrostrictive devicecomprising a driving portion to be driven by displacement of apiezoelectric/electrostrictive element, a movable portion to be operatedby displacement of said driving portion, a fixing portion for holdingsaid driving portion and said movable portion, said movable portionbeing coupled with said fixing portion via said driving portion, and ahole formed by inner walls of said driving portion, an inner wall ofsaid movable portion, and an inner wall of said fixing portion, saiddriving portion comprising a pair of mutually opposing thin plateportions, and a piezoelectric/electrostrictive element including apiezoelectric/electrostrictive operating portion comprising a pair ormore of electrodes and a piezoelectric/electrostrictive layer arrangedon at least a part of the outer surface of at least one of said thinplate portions, one end of said piezoelectric/electrostrictive operatingportion in a direction in which said fixing portion is connected withsaid movable portion exists on said fixing portion or said movableportion, and the other end of said piezoelectric/electrostrictiveoperating portion is arranged on said thin plate portion, and at leastone end of a piezoelectric/electrostrictive layer of saidpiezoelectric/electrostrictive element exists on said fixing portion orsaid movable portion, and the other end thereof is arranged on said thinplate portion, the Young's modulus Y1 of a material composing said thinplate portions and the Young's modulus Y2 of a material composing saidpiezoelectric/electrostrictive layer have a relationship satisfying thefollowing expression: 1<Y1/Y2≦20.
 2. A piezoelectric/electrostrictivedevice according to claim 1, wherein said movable portion, said thinplate portions, and said fixing portion are integrally formed bysimultaneously sintering a ceramic green laminated body.
 3. Apiezoelectric/electrostrictive device according to claim 1, wherein saidpiezoelectric/electrostrictive element is a film-likepiezoelectric/electrostrictive element first formed directly on saidthin plate portion and said movable portion or said fixing portion, andis then integrally formed by sintering.
 4. Apiezoelectric/electrostrictive device according to claim 3, wherein saidpiezoelectric/electrostrictive layer of said film-likepiezoelectric/electrostrictive element is free of glass frit.
 5. Apiezoelectric/electrostrictive device according to claim 1, wherein saidmovable portion displaces so as to satisfy the following expressionrelative to an angle, θ, formed by one side of said movable portionopposing to said fixing portion in a displaced state and the same oneside of said movable portion prior to the displacement, the expressionbeing: 0°≦θ≦0.1°.
 6. A piezoelectric/electrostrictive device accordingto claim 1, wherein the length, L, of a portion, arranged on said thinplate portion, of said piezoelectric/electrostrictive operating portionsatisfies the following expression relative to a relationship betweenthe length, e, of said thin plate portion, and the thickness, d, theexpression being: 30≦(L/e)×100≦100−d/2.5.
 7. Apiezoelectric/electrostrictive device according to claim 6, wherein, ina virtual circle having the center thereof on a perpendicular dropped tosaid fixing portion from the middle point of one side of said movableportion opposing to said fixing portion in a non-displaced state, andpassing through the middle point of the movable portion in saidnon-displaced state and the middle point of the movable portiondisplaced by operation of said driving portion, the movable portiondisplaces such that a relationship between the radius, r, of saidvirtual circle and the length, e, of said thin plate portion satisfiesthe following expression: 0≦e/r≦100, and when driven by displacement ofsaid piezoelectric/electrostrictive element, an inflection point for thedisplacement exists on said thin plate portion.
 8. Apiezoelectric/electrostrictive device according to claim 6, wherein thelength, L, of said piezoelectric/electrostrictive operating portionarranged on said thin plate portion satisfies the following expressionrelative to a relationship between the length, e, of said thin plateportion and the thickness, d, of said thin plate portion, the expressionbeing: 40≦(L/e)×100≦100−d/1.5.
 9. A piezoelectric/electrostrictivedevice according to claim 8, wherein, in a virtual circle having thecenter thereof on a perpendicular dropped to said fixing portion fromthe middle point of one side of said movable portion opposing to saidfixing portion in a non-displaced state, and passing through the middlepoint of said movable portion in said non-displaced state and the middlepoint of said movable portion displaced by operation of said drivingportion, said movable portion displaces such that a relationship betweenthe radius, r, of said virtual circle and the length, e, of said thinplate portion satisfies the following expression: 0≦e/r≦20, and aninflection point for the displacement of said thin plate portion existsat a position spaced by one half or more of the length of said thinplate portion from a joined portion between said thin plate portion andsaid fixing portion or said movable portion, thepiezoelectric/electrostrictive operating portion existing on either saidfixing portion or said movable portion.
 10. Apiezoelectric/electrostrictive device according to claim 1, wherein thethickness, a, of said hole and the length, e, of said thin plate portionhave a ratio expressed by e/a which is 0.1 to 2, and the thickness, a,of said hole and the width, b, of said thin plate portion have a ratioexpressed by a/b which is 0.05 to
 2. 11. Apiezoelectric/electrostrictive device according to claim 1, comprising aplurality of piezoelectric/electrostrictive elements, wherein at leastone of said piezoelectric/electrostrictive elements has a multi-layeredpiezoelectric/electrostrictive operating portion.